Downloaded from http://emj.bmj.com/ on December 22, 2014 - Published by group.bmj.com
Original article
Identification of the optimum vagal manoeuvre technique for maximising vagal tone Gavin Smith,1 Alicia Broek,2 David McD Taylor,3 Amee Morgans,4 Peter Cameron5 1
Department of Epidemiology and Preventative Medicine, Faculty of Medicine, Nursing, and Health Sciences, Alfred Centre, Monash University, Melbourne, Australia 2 Ambulance Victoria, Doncaster, Victoria, Australia 3 Austin Health, Heidelberg, Victoria, Australia 4 Monash University, Doncaster, Victoria, Australia 5 Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Victoria, Australia Correspondence to Gavin Smith, Department of Epidemiology and Preventive Medicine, Faculty of Medicine, Monash University, Nursing, and Health Sciences, Alfred Centre, 99 Commercial Road, Melbourne 3004, Australia; [email protected] Received 8 October 2013 Revised 6 May 2014 Accepted 14 May 2014 Published Online First 5 June 2014
ABSTRACT Objectives This study sought to determine the most effective technique for Valsalva Manoeuvre (VM) and Human Dive Reflex Manoeuvre (HDR) generation of vagal tone. Methods We conducted a repeated-measures trial of healthy adult volunteers from a university campus, aged 18–56 years, in sinus rhythm. Participants were randomised to VM (in supine or Trendelenberg postures) and HDR (supine or sitting postures) sequentially. Participants performed three trials of each technique, in random order, with a continuous ECG recording. Singleblinded analysis of ECG data was conducted. Mean differences between premanoeuvre and postmanoeuvre R-R intervals and heart rates were calculated for each posture within and between vagal manoeuvres. Results Seventy-two participants were enrolled. The difference between VM (supine) and VM (Trendelenberg) was not significant at 0.008 s (−0.023 to 0.038). The difference in mean R-R intervals for HDR (supine) was greater than HDR (sitting) 0.062 (0.031 to 0.093), although this significance was not reflected in a heartrate change of −0.87 (−3.00 to 1.26). VM supine generated greatest overall mean R-R interval difference, while HDR (sitting) provided the smallest change in R-R interval. The VM (supine) provided a significant maximum effectiveness over the HDR (supine) of 0.102 s (0.071 to 0.132). Conclusions This study demonstrates that VM (supine) generates the greatest vagal tone producing the largest transient heart rate decrease in healthy volunteers. No advantage was identified in Trendelenberg posturing for the VM in this study. These results may assist in the standardisation of vagal manoeuvre technique for the range of therapeutic and diagnostic applications.
INTRODUCTION
To cite: Smith G, Broek A, Taylor DMcD, et al. Emerg Med J 2015;32:51–54.
The first-line management of supraventricular tachycardia (SVT), and many other diagnostic and therapeutic techniques, involves the performance of a manoeuvre to increase vagal tone. Determining a simple and standardised vagal manoeuvre is important for prehospital and emergency medicine practice. Two commonly used vagal manoeuvres are the Valsalva Manoeuvre (VM) and the Human Dive Reflex (HDR). Taylor and Wong suggested that the optimum technique for the VM comprised supine posturing, an intrathoracic pressure of 40 mm Hg and duration of 15 s (table 1).1 They also investigated the effect on vagal tone of varying the posture and reported that the supine posture provided optimal vagal tone generation.2 However, in 2010, Walker and Cutting challenged this finding and suggested that a 15° head-down tilt (Trendelenberg position)
provided greater vagal tone (and hence, potential effectiveness in termination of SVT) than supine posturing in a sample of 19 patients.3 The original Wong and Taylor study did not employ the Trendelenberg posture,2 and Walker and Cutting’s work has not been replicated.3 Hence, the advantage of head-down posture has not been validated in further studies. The HDR is a physiological reflex originally observed in seals, among other aquatic mammals.4 Scientists observed the manner in which seals were able to preserve oxygen for use in prolonged dives through a cold-induced bradycardia and slowing of the metabolic processes, in combination with redirection of circulation to vital organs. This reflex was also noted in humans, where a cold stimulus applied solely to the face was found to elicit a reflex bradycardia.5 6 The HDR has demonstrated usefulness in terminating SVT through its effect in delaying AV nodal conduction. While the effectiveness of the HDR has been extensively studied,6–15 the absence of a standardised technique precludes a comparison of methods (table 1). Unlike the VM, the HDR has not been described in phases, but can be represented as an association of heart rate and peripheral vascular resistance over a relatively brief period of time. The VM is known to generate hypotensive episodes when performed by patients in an upright posture, thus supine posturing has been recommended.1 2 9 16–19 There are no studies describing this effect in the HDR, yet increased vagal tone during HDR performance would suggest that hypotension is a risk. The nature of the cold stimulus (applying an ice pack to the face or placing the patients face into a bowl of iced water) appears to have dictated the posture in available studies. The duration of the HDR varies considerably within studies of technique and effectiveness, and ranges from 15–35 s and 1–15 s in adult and paediatric patients with SVT, respectively.6–15 These studies also demonstrate a large variation in effectiveness, and this is likely to be attributable to variations in technique. Duration of the VM and HDR have previously been reported from studies that provide support for a standardised technique of VM duration of 15 s and HDR duration of 30 s being recommended.1 4 Posture remains a debated component with no single standard supported in the literature. Within available studies, the variation in performance technique, particularly the posture used, precludes identification of the vagal manoeuvre generating maximum vagal tone. The aim of this study was to compare the vagal responses generated by the VM and HDR in combination with postural
Smith G, et al. Emerg Med J 2015;32:51–54. doi:10.1136/emermed-2013-203299
51
Downloaded from http://emj.bmj.com/ on December 22, 2014 - Published by group.bmj.com
Original article Table 1
Vagal manoeuvre technique
Vagal manoeuvre
Valsalva
Human Dive Reflex
Technique Supine
Head-down (Trendelenberg)
Blow into a tube connected to a sphygmomanometer for 15 s to achieve a pressure of 40 mm Hg Supine Cold pack applied to patients face for 30 s
Blow into a tube connected to a sphygmomanometer for 15 s to achieve a pressure of 40 mm Hg Sitting Cold pack applied to patients face or face immersed in a bowl of iced water for 30 s
variation. The findings will identify the optimal vagal manoeuvre for maximising vagal tone generation.
METHODS The study was a repeated-measures, clinical trial of healthy adult volunteers from a university campus. It was conducted at Monash University, Victoria, Australia, between December 2012 and March 2013, and employed convenience sampling to recruit participants. Written consent was obtained by the investigators prior to enrolment, and each participant was given adequate time to read and understand the study protocol prior to participation. Monash University Human Research Ethics Committee approved the conduct of this study. Inclusion criteria were age between 18 and 60 years, sinus rhythm on the initial ECG, and self-reported good general health. Exclusion criteria were any regular medication (other than oral contraceptives), and a previous diagnosis of cardiovascular or respiratory disease. Participants were also requested to refrain from smoking, consuming alcohol or caffeine for the 6 h prior to testing. Testing was conducted indoors, with mean ambient room temperature over the 14 days of testing of mean 23.6° Celsius (median 23.4). Each participant performed three trials of four different techniques: VM supine and 15° head-down (Trendelenberg), and HDR supine and sitting. The trials were undertaken in a single session with the order of the 12 trials randomised separately for each participant using a computergenerated randomisation table. For the VM, participants were instructed to blow into a tube connected to a sphygmomanometer (with a specified air leak to prevent oral pressure only) and to maintain the pressure gauge at 40 mm Hg for 15 s. For the HDR, participants were instructed to place a cold gel-pack (mean temperature 4.3°C (median 4.2) over their face for 30 s while sitting in a chair or lying supine. The cold pack temperature of 4° Celsius was used to reflect normal refrigerator temperatures, a reported optimum temperature effectiveness of ≤10°C,4 and to avoid thermal injury as temperature approaches 0°C.4 8 20 A predetermined restitution period of 3 min between manoeuvres was used to enable cardiovascular and respiratory values to return to normal.2 During each trial, a continuous ECG was recorded (Lead II running at 25 mm/second via the Phillips HeartStart MRx monitor/defibrillator (Koninklijke Philips Electronics 2004). The monitor was calibrated daily prior to commencement of testing. Points denoting the start and end of each trial were marked on the ECG strip to enable reference for later analysis by an investigator (AB), who was blinded to the technique undertaken. Using the ECG R-R interval as an indirect measurement of vagal tone, linear R-R intervals (measured in mm) were measured directly from the ECG strip using a ruler, and subsequently converted to a time period (measured in seconds). The premanoeuvre R-R interval was calculated using the mean of 10 52
consecutive R-R intervals preceding the onset of each manoeuvre. The postmanoeuvre R-R interval was the single longest R-R interval within 15 s of termination of the manoeuvre, as described by Wong and Taylor.2 Intervals where a premature ectopic complex resulted in a compensatory pause were excluded from the premanoeuvre R-R interval measurement. Where this occurred, the next immediate R-R interval was added. The study endpoints were the mean difference in R-R interval (postvalue minus prevalue, in seconds) the mean difference in heart rate ( postvalue minus prevalue, in beats per minute) calculated from the three trials of each manoeuvre/posture variation, with baseline values used as a covariate. The mean differences between manoeuvre types were compared. The mean difference between the VM and HDR techniques that generated the longest R-R intervals (and greatest decrease in heart rate) were also compared. It is difficult to determine a clinically significant difference in mean heart rates between manoeuvres. However, an a priori F-test (repeated measures, within-between interaction) of difference of mean heart rates based upon the Wong and Taylor2 study was performed using G*Power 3.1.3 software.21 Using a mean heart rate difference between techniques of 3 beats/min (as described in the Wong and Taylor study), and in the absence of other evidence to support clinically significant changes in heart rate, a sample size of at least 68 participants was required (power 0.8; level of significance 0.05, within-person correlation across measures 0.8, effect size 0.12). For each vagal manoeuvre technique tested, mean values were calculated with 95% CIs. Following assessment for normal distribution of the data, linear mixed effects regression was used to model both primary outcomes. For each model the difference in RR ( postvalue minus prevalue) was the outcome, with type of manoeuvre and baseline RR interval treated as a fixed effect and participant as a random effect. Using the resulting models, pairwise comparisons were made between the four different manoeuvre types. The Bonferroni correction was applied to the pairwise comparisons to adjust for the number of statistical tests by multiplying the p value for each pairwise t test by six (the number of comparisons). A p value must reach 0.05 to be declared statistically significant. Statistical analysis was undertaken by GS, and completed using SPSS (Statistical Package for the Social Sciences V.20.0, SPSS, Chicago, Illinois, USA) software. Independent analysis was also undertaken by a consultant statistician.
RESULTS A total of 72 participants were enrolled. One participant developed ventricular ectopic activity early in the first strain test. This condition was known to the participant, but had not been disclosed during enrolment. Another participant had abnormalities detected on baseline ECG. Both these participants were excluded from the study. The mean age of the remaining Smith G, et al. Emerg Med J 2015;32:51–54. doi:10.1136/emermed-2013-203299
Downloaded from http://emj.bmj.com/ on December 22, 2014 - Published by group.bmj.com
Original article Table 2 Mean premanoeuvre, postmanoeuvre and difference values for each technique Manoeuvre
Mean premanoeuvre R-R interval (SD)*
Mean postmanoeuvre R-R interval (SD)*
Mean R-R interval difference (SD)*
Mean premanoeuvre heart rate (SD)†
Mean postmanoeuvre heart rate (SD)†
Mean heart rate difference (SD)†
VM (supine) VM (head-down) HDR (supine) HDR (sitting)
0.845 0.843 0.884 0.842
1.143 1.135 1.051 0.978
0.298 0.291 0.167 0.136
73.0 (12.4) 72.9 (12.0) 69.4 (10.2) 73.0 (11.5)
54.1 54.7 58.7 63.2
−18.97 −18.29 −10.71 −9.84
(0.142) (0.142) (0.134) (0.134)
(0.202) (0.209) (0.183) (0.173)
(0.203) (0.194) (0.126) (0.111)
(9.7) (10.2) (10.2) (11.2)
(12.51) (11.68) (7.12) (7.11)
*Measured in seconds. †Measured in beats per minute.
participants was 27.8±9.1 years (range 18 to 56 years), including 35 men (50%). No participants were resistive to the testing procedure (either blowing into the pressure device or applying a cold pack to their face). The mean premanoeuvre and postmanoeuvre R-R intervals, mean premanoeuvre and postmanoeuvre heart rates and mean change for each of the four techniques are reported in table 2. Each technique resulted in significant increases in the R-R intervals postmanoeuvre. The mean pre/post difference in R-R interval was greatest for the VM (supine) and smallest for the HDR (sitting), as demonstrated in table 2. Comparison of mean R-R interval difference between VM (supine) and VM (head-down) suggested no statistically significant difference between postures (table 3). There was no statistical significance demonstrated between the heart rate change in HDR (supine) and HDR (sitting) postures, although the increase in R-R interval was found to be statistically significant. The VM (supine) provided significantly greater mean R-R interval difference and heart rate difference than the HDR (supine). The mean change from premanoeuvre to postmanoeuvre was found to be significant between manoeuvre types measured for time (seconds) where F (3, 760.6)=94.690, p
Original article
Identification of the optimum vagal manoeuvre technique for maximising vagal tone Gavin Smith,1 Alicia Broek,2 David McD Taylor,3 Amee Morgans,4 Peter Cameron5 1
Department of Epidemiology and Preventative Medicine, Faculty of Medicine, Nursing, and Health Sciences, Alfred Centre, Monash University, Melbourne, Australia 2 Ambulance Victoria, Doncaster, Victoria, Australia 3 Austin Health, Heidelberg, Victoria, Australia 4 Monash University, Doncaster, Victoria, Australia 5 Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Victoria, Australia Correspondence to Gavin Smith, Department of Epidemiology and Preventive Medicine, Faculty of Medicine, Monash University, Nursing, and Health Sciences, Alfred Centre, 99 Commercial Road, Melbourne 3004, Australia; [email protected] Received 8 October 2013 Revised 6 May 2014 Accepted 14 May 2014 Published Online First 5 June 2014
ABSTRACT Objectives This study sought to determine the most effective technique for Valsalva Manoeuvre (VM) and Human Dive Reflex Manoeuvre (HDR) generation of vagal tone. Methods We conducted a repeated-measures trial of healthy adult volunteers from a university campus, aged 18–56 years, in sinus rhythm. Participants were randomised to VM (in supine or Trendelenberg postures) and HDR (supine or sitting postures) sequentially. Participants performed three trials of each technique, in random order, with a continuous ECG recording. Singleblinded analysis of ECG data was conducted. Mean differences between premanoeuvre and postmanoeuvre R-R intervals and heart rates were calculated for each posture within and between vagal manoeuvres. Results Seventy-two participants were enrolled. The difference between VM (supine) and VM (Trendelenberg) was not significant at 0.008 s (−0.023 to 0.038). The difference in mean R-R intervals for HDR (supine) was greater than HDR (sitting) 0.062 (0.031 to 0.093), although this significance was not reflected in a heartrate change of −0.87 (−3.00 to 1.26). VM supine generated greatest overall mean R-R interval difference, while HDR (sitting) provided the smallest change in R-R interval. The VM (supine) provided a significant maximum effectiveness over the HDR (supine) of 0.102 s (0.071 to 0.132). Conclusions This study demonstrates that VM (supine) generates the greatest vagal tone producing the largest transient heart rate decrease in healthy volunteers. No advantage was identified in Trendelenberg posturing for the VM in this study. These results may assist in the standardisation of vagal manoeuvre technique for the range of therapeutic and diagnostic applications.
INTRODUCTION
To cite: Smith G, Broek A, Taylor DMcD, et al. Emerg Med J 2015;32:51–54.
The first-line management of supraventricular tachycardia (SVT), and many other diagnostic and therapeutic techniques, involves the performance of a manoeuvre to increase vagal tone. Determining a simple and standardised vagal manoeuvre is important for prehospital and emergency medicine practice. Two commonly used vagal manoeuvres are the Valsalva Manoeuvre (VM) and the Human Dive Reflex (HDR). Taylor and Wong suggested that the optimum technique for the VM comprised supine posturing, an intrathoracic pressure of 40 mm Hg and duration of 15 s (table 1).1 They also investigated the effect on vagal tone of varying the posture and reported that the supine posture provided optimal vagal tone generation.2 However, in 2010, Walker and Cutting challenged this finding and suggested that a 15° head-down tilt (Trendelenberg position)
provided greater vagal tone (and hence, potential effectiveness in termination of SVT) than supine posturing in a sample of 19 patients.3 The original Wong and Taylor study did not employ the Trendelenberg posture,2 and Walker and Cutting’s work has not been replicated.3 Hence, the advantage of head-down posture has not been validated in further studies. The HDR is a physiological reflex originally observed in seals, among other aquatic mammals.4 Scientists observed the manner in which seals were able to preserve oxygen for use in prolonged dives through a cold-induced bradycardia and slowing of the metabolic processes, in combination with redirection of circulation to vital organs. This reflex was also noted in humans, where a cold stimulus applied solely to the face was found to elicit a reflex bradycardia.5 6 The HDR has demonstrated usefulness in terminating SVT through its effect in delaying AV nodal conduction. While the effectiveness of the HDR has been extensively studied,6–15 the absence of a standardised technique precludes a comparison of methods (table 1). Unlike the VM, the HDR has not been described in phases, but can be represented as an association of heart rate and peripheral vascular resistance over a relatively brief period of time. The VM is known to generate hypotensive episodes when performed by patients in an upright posture, thus supine posturing has been recommended.1 2 9 16–19 There are no studies describing this effect in the HDR, yet increased vagal tone during HDR performance would suggest that hypotension is a risk. The nature of the cold stimulus (applying an ice pack to the face or placing the patients face into a bowl of iced water) appears to have dictated the posture in available studies. The duration of the HDR varies considerably within studies of technique and effectiveness, and ranges from 15–35 s and 1–15 s in adult and paediatric patients with SVT, respectively.6–15 These studies also demonstrate a large variation in effectiveness, and this is likely to be attributable to variations in technique. Duration of the VM and HDR have previously been reported from studies that provide support for a standardised technique of VM duration of 15 s and HDR duration of 30 s being recommended.1 4 Posture remains a debated component with no single standard supported in the literature. Within available studies, the variation in performance technique, particularly the posture used, precludes identification of the vagal manoeuvre generating maximum vagal tone. The aim of this study was to compare the vagal responses generated by the VM and HDR in combination with postural
Smith G, et al. Emerg Med J 2015;32:51–54. doi:10.1136/emermed-2013-203299
51
Downloaded from http://emj.bmj.com/ on December 22, 2014 - Published by group.bmj.com
Original article Table 1
Vagal manoeuvre technique
Vagal manoeuvre
Valsalva
Human Dive Reflex
Technique Supine
Head-down (Trendelenberg)
Blow into a tube connected to a sphygmomanometer for 15 s to achieve a pressure of 40 mm Hg Supine Cold pack applied to patients face for 30 s
Blow into a tube connected to a sphygmomanometer for 15 s to achieve a pressure of 40 mm Hg Sitting Cold pack applied to patients face or face immersed in a bowl of iced water for 30 s
variation. The findings will identify the optimal vagal manoeuvre for maximising vagal tone generation.
METHODS The study was a repeated-measures, clinical trial of healthy adult volunteers from a university campus. It was conducted at Monash University, Victoria, Australia, between December 2012 and March 2013, and employed convenience sampling to recruit participants. Written consent was obtained by the investigators prior to enrolment, and each participant was given adequate time to read and understand the study protocol prior to participation. Monash University Human Research Ethics Committee approved the conduct of this study. Inclusion criteria were age between 18 and 60 years, sinus rhythm on the initial ECG, and self-reported good general health. Exclusion criteria were any regular medication (other than oral contraceptives), and a previous diagnosis of cardiovascular or respiratory disease. Participants were also requested to refrain from smoking, consuming alcohol or caffeine for the 6 h prior to testing. Testing was conducted indoors, with mean ambient room temperature over the 14 days of testing of mean 23.6° Celsius (median 23.4). Each participant performed three trials of four different techniques: VM supine and 15° head-down (Trendelenberg), and HDR supine and sitting. The trials were undertaken in a single session with the order of the 12 trials randomised separately for each participant using a computergenerated randomisation table. For the VM, participants were instructed to blow into a tube connected to a sphygmomanometer (with a specified air leak to prevent oral pressure only) and to maintain the pressure gauge at 40 mm Hg for 15 s. For the HDR, participants were instructed to place a cold gel-pack (mean temperature 4.3°C (median 4.2) over their face for 30 s while sitting in a chair or lying supine. The cold pack temperature of 4° Celsius was used to reflect normal refrigerator temperatures, a reported optimum temperature effectiveness of ≤10°C,4 and to avoid thermal injury as temperature approaches 0°C.4 8 20 A predetermined restitution period of 3 min between manoeuvres was used to enable cardiovascular and respiratory values to return to normal.2 During each trial, a continuous ECG was recorded (Lead II running at 25 mm/second via the Phillips HeartStart MRx monitor/defibrillator (Koninklijke Philips Electronics 2004). The monitor was calibrated daily prior to commencement of testing. Points denoting the start and end of each trial were marked on the ECG strip to enable reference for later analysis by an investigator (AB), who was blinded to the technique undertaken. Using the ECG R-R interval as an indirect measurement of vagal tone, linear R-R intervals (measured in mm) were measured directly from the ECG strip using a ruler, and subsequently converted to a time period (measured in seconds). The premanoeuvre R-R interval was calculated using the mean of 10 52
consecutive R-R intervals preceding the onset of each manoeuvre. The postmanoeuvre R-R interval was the single longest R-R interval within 15 s of termination of the manoeuvre, as described by Wong and Taylor.2 Intervals where a premature ectopic complex resulted in a compensatory pause were excluded from the premanoeuvre R-R interval measurement. Where this occurred, the next immediate R-R interval was added. The study endpoints were the mean difference in R-R interval (postvalue minus prevalue, in seconds) the mean difference in heart rate ( postvalue minus prevalue, in beats per minute) calculated from the three trials of each manoeuvre/posture variation, with baseline values used as a covariate. The mean differences between manoeuvre types were compared. The mean difference between the VM and HDR techniques that generated the longest R-R intervals (and greatest decrease in heart rate) were also compared. It is difficult to determine a clinically significant difference in mean heart rates between manoeuvres. However, an a priori F-test (repeated measures, within-between interaction) of difference of mean heart rates based upon the Wong and Taylor2 study was performed using G*Power 3.1.3 software.21 Using a mean heart rate difference between techniques of 3 beats/min (as described in the Wong and Taylor study), and in the absence of other evidence to support clinically significant changes in heart rate, a sample size of at least 68 participants was required (power 0.8; level of significance 0.05, within-person correlation across measures 0.8, effect size 0.12). For each vagal manoeuvre technique tested, mean values were calculated with 95% CIs. Following assessment for normal distribution of the data, linear mixed effects regression was used to model both primary outcomes. For each model the difference in RR ( postvalue minus prevalue) was the outcome, with type of manoeuvre and baseline RR interval treated as a fixed effect and participant as a random effect. Using the resulting models, pairwise comparisons were made between the four different manoeuvre types. The Bonferroni correction was applied to the pairwise comparisons to adjust for the number of statistical tests by multiplying the p value for each pairwise t test by six (the number of comparisons). A p value must reach 0.05 to be declared statistically significant. Statistical analysis was undertaken by GS, and completed using SPSS (Statistical Package for the Social Sciences V.20.0, SPSS, Chicago, Illinois, USA) software. Independent analysis was also undertaken by a consultant statistician.
RESULTS A total of 72 participants were enrolled. One participant developed ventricular ectopic activity early in the first strain test. This condition was known to the participant, but had not been disclosed during enrolment. Another participant had abnormalities detected on baseline ECG. Both these participants were excluded from the study. The mean age of the remaining Smith G, et al. Emerg Med J 2015;32:51–54. doi:10.1136/emermed-2013-203299
Downloaded from http://emj.bmj.com/ on December 22, 2014 - Published by group.bmj.com
Original article Table 2 Mean premanoeuvre, postmanoeuvre and difference values for each technique Manoeuvre
Mean premanoeuvre R-R interval (SD)*
Mean postmanoeuvre R-R interval (SD)*
Mean R-R interval difference (SD)*
Mean premanoeuvre heart rate (SD)†
Mean postmanoeuvre heart rate (SD)†
Mean heart rate difference (SD)†
VM (supine) VM (head-down) HDR (supine) HDR (sitting)
0.845 0.843 0.884 0.842
1.143 1.135 1.051 0.978
0.298 0.291 0.167 0.136
73.0 (12.4) 72.9 (12.0) 69.4 (10.2) 73.0 (11.5)
54.1 54.7 58.7 63.2
−18.97 −18.29 −10.71 −9.84
(0.142) (0.142) (0.134) (0.134)
(0.202) (0.209) (0.183) (0.173)
(0.203) (0.194) (0.126) (0.111)
(9.7) (10.2) (10.2) (11.2)
(12.51) (11.68) (7.12) (7.11)
*Measured in seconds. †Measured in beats per minute.
participants was 27.8±9.1 years (range 18 to 56 years), including 35 men (50%). No participants were resistive to the testing procedure (either blowing into the pressure device or applying a cold pack to their face). The mean premanoeuvre and postmanoeuvre R-R intervals, mean premanoeuvre and postmanoeuvre heart rates and mean change for each of the four techniques are reported in table 2. Each technique resulted in significant increases in the R-R intervals postmanoeuvre. The mean pre/post difference in R-R interval was greatest for the VM (supine) and smallest for the HDR (sitting), as demonstrated in table 2. Comparison of mean R-R interval difference between VM (supine) and VM (head-down) suggested no statistically significant difference between postures (table 3). There was no statistical significance demonstrated between the heart rate change in HDR (supine) and HDR (sitting) postures, although the increase in R-R interval was found to be statistically significant. The VM (supine) provided significantly greater mean R-R interval difference and heart rate difference than the HDR (supine). The mean change from premanoeuvre to postmanoeuvre was found to be significant between manoeuvre types measured for time (seconds) where F (3, 760.6)=94.690, p
