Arterial pressure response to maximal isometric exercise in pregnant women Fred K. Lotgering, Lotgering. MD, PhD, Akkeliene van den Berg, Berg. BSe, Piet C. Struijk, BSe, and Henk C.S. Wallenburg, MD, PhD Rotterdam, The Netherlands We studied the arterial pressure response to maximal leg exercise in 15 healthy volunteers at 29 and 35 weeks' pregnancy and at 8 weeks post partum. Resting mean arterial pressure at 35 weeks' gestation was similar to the postpartum control value of 88 mm Hg (range 73 to 111), but it was reduced by 10% at 29 weeks' gestation. Voluntary maximal effort averaged 2470 N (range 1450 to 3030) in the postpartum period, was similar at 29 weeks, and was reduced by 13% at 35 weeks' gestation. gestation. Mean arterial pressure showed a linear increase with force to a median maximum value of 131 (104 to 159) mm Hg, or 49% above the resting value in the postpartum period. The pressure response was unaffected by pregnancy, but was inversely related to maximal force, i.e., the individual's capacity to perform isometric exercise. (AM J OBSTET GVNECOL 1992;166:538-42.)
Key words: Pregnancy, maximal exercise, isometric exercise, blood pressure
Pregnancy and muscular exercise require physiologic adaptations to increase blood flow to the regions of the body with increased metabolic activity: the uterus and the exercising muscles. The cardiovascular responses to pregnancy and to dynamic exercise include an increase in cardiac output, through increases in heart rate and stroke volume, with a reduction in peripheral vascular resistance. As a net result of these changes, systemic blood pressure usually falls slightly during pregnancy, whereas it increases mildly during dynamic d ynamic exercise. 1 The adaptations are so effective that the ercise.' combined demands of pregnancy and dynamic exercise do not appear to compromise the healthy fetus fetus'"l -' nor affect the capability of healthy pregnant women to perform dynamic aerobic exercise.' In contrast to dynamic exercise in which muscles undergo shortening or lengthening, isometric exercise does not result in muscle movement. Sustained muscle activity not only induces local vasodilatation but also muscle ischemia and mechanical obstruction to muscle perfusion.' Therefore, isometric exercise elicits a different cardiovascular response, response , with a more pronounced increase in arterial pressure than that during dynamic exercise. The mechanisms of these responses have recently been reviewed 5 and will be discussed in Comments. The magnitude of the response is de penFrom the Department of Obstetrics and and Gynecology, Erasmus University School of Medicine and Health H ealth Sciences. Received R eceived for publication September 19, 1990; revised revised May Ma,V31, 31 , 1991; 1991 ; accepted July 17,1991. Reprint R eprint requests: requests: Fred K. Lotgering, Lo/gering, MD, MD, PhD, PhD, Department Department of Obstetrics and Gynecology, EE 2283, Erasmus University School of M edicine and Health Sciences, P.O. Medicine P .O.Box 1738, 3000 DR Rotterdam, The Netherlands. 611132442
dent on the strength and duration of muscular contraction.' traction" The combined effect of isometric exercise and pregnancy has only been studied by means of handgrip exercise. 6 .-s However, in handgrip exercise the active muscle mass is relatively small and the required force cannot be accurately determined. determined . In the present longitudinal study we investigated the effects of pregnancy on the capability of the body to perform strenuous isometric exercise, and we determined blood pressure and heart hea("t rate ("esponses responses to such exercise.
Material and methods We studied 15 healthy women at 29 and 35 weeks of pregnancy and at 8 weeks post partum. All women were healthy, normotensive, and had uncomplicated singleton pregnancies, but they varied with regard to body weight and physical fitness. All women included in the study gave their informed consent. consent. The study was approved by by the Hospital and University Ethics Committee. The women performed isometric exercise in an airconditioned room kept at 21 0 C and at 60% humidity. humidity. Before each test we performed a routine physical and obstetric examination and monitored fetal heart rate (Corometrics, Fetal monitor Ill, Ill , Wallingford, Conn.) to confirm the health of both individuals participating in the study. In addition, we determined body weight and leg length, from heel to trochanter major. The woman was placed on an ergometer designed for this study (Central Research Workshop, Workshop, EUR, Rotterdam, the Netherlands). Netherlands). It consisted of a chair with a horifootboard.. The distance between the zontal, adjustable footboard back of the chair and the footboard was adjusted to 0
Maximal isometric exercise in pregnancy 539
Volume 166 Number 2
Table I. Effects of pregnancy on values at rest and at maximal isometric leg exercise
At rest 29 weeks 35 weeks Post partum Maximum 29 weeks 35 weeks Post partum
Blood pressure (mm Hg)
Heart rate (beats I min)
Systolic
92* (86-107) 90* (72-101) 78 (60-94)
112* (91-130) 119 (100-129) 119 (102-135)
79* (74-101) 87 (73-93) 88 (73-111)
68* (54-84) 74 (53-81) 76 (61-93)
131 * (108-163) 122* (98-170) 119 (93-156)
147 (133-173) 145 (127-181) 153 (127-181)
122 (101-145) 123 (106-155) 131 (104-159)
108 (92-126) 108 (90-132) 115 (90-137)
I
Mean
I
Diastolic
Force (N)
2400 (1470-3160) 2160* (1400-2800) 2470 (1450-3030)
Median values with ranges in brackets.
*p < 0.05 compared with postpartum control values, n
='
90% of the length of the woman's legs and was kept constant between measurements within each individual. After 15 minutes of rest on the ergometer, the force exerted on the footboard was progressively and stepwise increased by 400 N per increment, until voluntary maximum effort was reached. Efforts of 45 seconds' duration were separated by 2 minutes of rest. The force exerted on the footboard was measured electronically with calibrated strain gauges and found to be accurate within 1% over the full range of measured forces. Heart rate and systolic, mean, and diastolic arterial blood pressures were measured oscillometrically (Dinamap 845, Applied Medical, Tampa, Fla.), a method validated for the observed range of measurements. 9 Measurements took 20 to 45 seconds to be completed and were initiated 2 minutes before and at the onset of exercise. During the exercise the volunteer was encouraged to continue to breathe normally and not to use her arm muscles. Each woman underwent an initial test to get used to the experimental circumstances; the data obtained in this test were discarded. The Friedman and Wilcoxon ranked-sign tests were used to analyze differences between paired variables. Linear regression analysis was used to assess relationships between variables within each individual; the slopes and intercepts were treated as variables. A p value of
Key words: Pregnancy, maximal exercise, isometric exercise, blood pressure
Pregnancy and muscular exercise require physiologic adaptations to increase blood flow to the regions of the body with increased metabolic activity: the uterus and the exercising muscles. The cardiovascular responses to pregnancy and to dynamic exercise include an increase in cardiac output, through increases in heart rate and stroke volume, with a reduction in peripheral vascular resistance. As a net result of these changes, systemic blood pressure usually falls slightly during pregnancy, whereas it increases mildly during dynamic d ynamic exercise. 1 The adaptations are so effective that the ercise.' combined demands of pregnancy and dynamic exercise do not appear to compromise the healthy fetus fetus'"l -' nor affect the capability of healthy pregnant women to perform dynamic aerobic exercise.' In contrast to dynamic exercise in which muscles undergo shortening or lengthening, isometric exercise does not result in muscle movement. Sustained muscle activity not only induces local vasodilatation but also muscle ischemia and mechanical obstruction to muscle perfusion.' Therefore, isometric exercise elicits a different cardiovascular response, response , with a more pronounced increase in arterial pressure than that during dynamic exercise. The mechanisms of these responses have recently been reviewed 5 and will be discussed in Comments. The magnitude of the response is de penFrom the Department of Obstetrics and and Gynecology, Erasmus University School of Medicine and Health H ealth Sciences. Received R eceived for publication September 19, 1990; revised revised May Ma,V31, 31 , 1991; 1991 ; accepted July 17,1991. Reprint R eprint requests: requests: Fred K. Lotgering, Lo/gering, MD, MD, PhD, PhD, Department Department of Obstetrics and Gynecology, EE 2283, Erasmus University School of M edicine and Health Sciences, P.O. Medicine P .O.Box 1738, 3000 DR Rotterdam, The Netherlands. 611132442
dent on the strength and duration of muscular contraction.' traction" The combined effect of isometric exercise and pregnancy has only been studied by means of handgrip exercise. 6 .-s However, in handgrip exercise the active muscle mass is relatively small and the required force cannot be accurately determined. determined . In the present longitudinal study we investigated the effects of pregnancy on the capability of the body to perform strenuous isometric exercise, and we determined blood pressure and heart hea("t rate ("esponses responses to such exercise.
Material and methods We studied 15 healthy women at 29 and 35 weeks of pregnancy and at 8 weeks post partum. All women were healthy, normotensive, and had uncomplicated singleton pregnancies, but they varied with regard to body weight and physical fitness. All women included in the study gave their informed consent. consent. The study was approved by by the Hospital and University Ethics Committee. The women performed isometric exercise in an airconditioned room kept at 21 0 C and at 60% humidity. humidity. Before each test we performed a routine physical and obstetric examination and monitored fetal heart rate (Corometrics, Fetal monitor Ill, Ill , Wallingford, Conn.) to confirm the health of both individuals participating in the study. In addition, we determined body weight and leg length, from heel to trochanter major. The woman was placed on an ergometer designed for this study (Central Research Workshop, Workshop, EUR, Rotterdam, the Netherlands). Netherlands). It consisted of a chair with a horifootboard.. The distance between the zontal, adjustable footboard back of the chair and the footboard was adjusted to 0
Maximal isometric exercise in pregnancy 539
Volume 166 Number 2
Table I. Effects of pregnancy on values at rest and at maximal isometric leg exercise
At rest 29 weeks 35 weeks Post partum Maximum 29 weeks 35 weeks Post partum
Blood pressure (mm Hg)
Heart rate (beats I min)
Systolic
92* (86-107) 90* (72-101) 78 (60-94)
112* (91-130) 119 (100-129) 119 (102-135)
79* (74-101) 87 (73-93) 88 (73-111)
68* (54-84) 74 (53-81) 76 (61-93)
131 * (108-163) 122* (98-170) 119 (93-156)
147 (133-173) 145 (127-181) 153 (127-181)
122 (101-145) 123 (106-155) 131 (104-159)
108 (92-126) 108 (90-132) 115 (90-137)
I
Mean
I
Diastolic
Force (N)
2400 (1470-3160) 2160* (1400-2800) 2470 (1450-3030)
Median values with ranges in brackets.
*p < 0.05 compared with postpartum control values, n
='
90% of the length of the woman's legs and was kept constant between measurements within each individual. After 15 minutes of rest on the ergometer, the force exerted on the footboard was progressively and stepwise increased by 400 N per increment, until voluntary maximum effort was reached. Efforts of 45 seconds' duration were separated by 2 minutes of rest. The force exerted on the footboard was measured electronically with calibrated strain gauges and found to be accurate within 1% over the full range of measured forces. Heart rate and systolic, mean, and diastolic arterial blood pressures were measured oscillometrically (Dinamap 845, Applied Medical, Tampa, Fla.), a method validated for the observed range of measurements. 9 Measurements took 20 to 45 seconds to be completed and were initiated 2 minutes before and at the onset of exercise. During the exercise the volunteer was encouraged to continue to breathe normally and not to use her arm muscles. Each woman underwent an initial test to get used to the experimental circumstances; the data obtained in this test were discarded. The Friedman and Wilcoxon ranked-sign tests were used to analyze differences between paired variables. Linear regression analysis was used to assess relationships between variables within each individual; the slopes and intercepts were treated as variables. A p value of
