Basic data underlying clinical decisionmaking in vascular surgery Section Editor - John M. Porter, MD (Portland, Oregon)
Lower Extremity Venous Hemodynamics G. Belcaro, D. Christopoulos, A.N. Nicolaides, London, England
Chronic venous insufficiency may be the result of outflow obstruction, reflux or a combination of both. The first question the doctor asks is whether obstruction or reflux are present. The second question is where they are anatomically, if present. The third is how much obstruction or reflux exists (Table I). This last question can be answered in terms of hemodynamics. The tables below list the normal and abnormal hemodynamic values for different anatomically defined conditions. Ambulatory venous pressure (Table II) is defined as the lowest pressure during a ten tiptoe exercise. It is the oldest diagnostic quantitative test. Ambulatory venous pressure will be high in the presence of popliteal reflux (Table III). For ambulatory venous pressure from 40 to 80 there is a linear relationship with the incidence of ulceration irrespective of what (obstruction or reflux) and where it is (superficial or deep) (Table IV). Ambulatory venous pressure reflects the net effect of all abnormalities that affect hemodynamics. Photoplethysmographic (PPG) refilling time is similar to ambulatory venous pressure-refilling time. It can identify normal limbs and limbs with superficial and deep venous disease (Table V), However, it is a poor measure of the severity of deep venous disease. Ambulatory venous pressure may be in the range of 45-90 mmHg while the PPG-refilling time is very short (< l0 sec). In this situation a reduction in ambulatory venous pressure (for example, as a result of valve transplantation) will have little effect, if any, on refilling time. From the Irvine Laboratory for Cardiovascular Investigation and Research, Academic Surgical Unit, St. Mary's Hospital Medical School, London, England. Reprint requests: Andrew N. Nicolaides, Irvine Laboratory for Cardiovascular Investigation and Research, Academic Surgical Unit, St. Mary's Hospital Medical School, Praed Street, London W2 1PG, England.
Air-plethysmography provides quantitative information about the various components of the calf muscle pump (Table VI): the amount of blood in the reservoir (venous volume), the stroke volume of single step (ejected volume), the ejection fraction, the amount of reflux in ml/sec (VFI) and finally the residual volume (RV) as a result of t e n tiptoe movement. The residual volume fraction is linearly related to the ambulatory venous pressure and provides an indirect method to measure ambulatory venous pressure noninvasively. Tables VII-IX show the relationship between the air-plethysmographic parameters and the incidence of chronic swelling, skin changes and ulceration. The arm/foot pressure differential (Ap) with needles in arm and foot veins when the patient is horizontal is the most direct method of assessing the severity of outflow obstruction (Table X). The maximum venous outflow (MVO) using strain gauge plethysmography and one second outflow fraction (OF) using air-plethysmography are noninvasive methods of assessing obstruction (Table XI). The relationship between arm/foot pressure differential (Ap) and OF is shown in Table XII. The immediate and long-term effects of elastic compression on venous hemodynamics are shown in Tables XIII and XIV. It appears that graduated elastic compression reduces ambulatory venous pressure by decreasing reflux and increasing the ejection fraction, resulting in a reduced residual volume fraction. The latter is the amount of blood in the calf and determines the ambulatory venous pressure. The improved hemodynamics persist when the compression is removed and the limb retested four weeks later. Venous hypertensive microangiopathy is the result of chronic venous hypertension. It consists of an increased skin blood flow and a reduction in the venoarteriolar reflex. The latter is a physiological vasoconstrictory response to standing, it prevents
305
LOWER EXTREMITY VENOUS HEMOD YNAMICS
306
high pressure and flow in the capillary bed. In the presence of hypertensive microangiopathy, the high flow is associated with an increased capillary permeability and rate of ankle swelling on standing. Transcutaneous PO 2 measurements are related to the number of nutrient capillary loops open and not to overall blood flow (fibrosis and edema tend to obliterate them). However, because of the high diffusion rate of CO2, transcutaneous PCO 2 measurements are related to overall skin blood flow. Therapeutic methods that improve venous hemodynamics and venous hypertension, improve the microcirculation. The measurements shown in Table XV are providing a means of studying and understanding the microcirculation and associated skin changes in the gaiter area of the leg. TABLE I.--Grades of reflux in the deep veins on descending venography [1,2] Grade 0
Grade 1 Grade 2 Grade 3 Grade 4
No reflux below the confluence of the superficial and profunda femoris veins, i.e. the uppermost valve of the superficial femoral vein is competent. Reflux beyond the uppermost valve of the superficial femoral vein but not below the middle of the thigh. Reflux into the superficial femoral vein to the level of the knee. Popliteal valves competent. Reflux to a level just below the knee. Incompetent popliteal valves but competent valves in the axial calf veins. Reflux through the axial veins (femoral, popliteal and calf veins) to the level of the ankle.
ANNALS OF VASCULAR SURGERY
TABLE IIl.--Relationship between venographic grades of reflux in the deep veins, ambulatory venous pressure and refilling time [4]
Grades 0-2 Grades 3-4
AVP* (mmHg) No ankle Ankle cuff cuff
RTgot (sec) No ankle Ankle cuff cuff
30-70 50-95
2-15 1-8
10-45 40-90
13-45 2-14
*AVP = ambulatory venous pressure tRTgo = refilling time
TABLE IV.--The incidence of active or healed ulceration in relation to ambulatory venous pressure in 251 limbs [5] II
P(mmHg)
34 44 51 45 34 28 15
80
Incidence of ulceration (%) 0 12 20 38 57 68 73
TABLE V.--Photoplethysmographic refilling time without and with an ankle cuff to occlude the superficial veins [6] Standing No ankle Ankle cuff cuff Normal SVI t DVI ~
18-80* 5-18 3-12
Sitting No ankle Ankle cuff cuff
18-80 18-50 618"*
26-100 2-25 2-28
26-100 18-50 2-30
*RTgo > 18 sec without cuff identifies normal limbs. tSVI = superficial venous insufficiency ~DVI = deep venous insufficiency **RTgo < 18 sec with cuff identifies limbs with deep venous disease
TABLE II.--Ambulatory venous pressure and refilling time measured with cannulation of the foot vein [3]* AVP t (mmHg) Type of limb Normal Primary varicose veins with competent performating veins Primary varicose veins with incompetent perforating veins Deep venous reflux (incompetent popliteal valves) Popliteal reflux and proximal occlusion Proximal occlusion and competent popliteal valves
No ankle cuff
RTgow (sec) Ankle cuff
No ankle cuff. 18-40 10-18
Ankle cuff
15-30 25-40
15-30 15-30
40-70
25-60**
5-15
8-30**
55-85
50--80
3-15
5-15
60-110
60-120
--
--
25-60
10-60
--
--
*Standard exercise: 10 tiptoe movements tAmbulatory venous pressure w time **In one-third of these limbs AVP remained more than 40 mmHg and RT9o less than 15 seconds despite the application of the ankle cuff.
18-40 18-35
VOLUME 5 N o 3 - 1991
LOWER EXTREMITY VENOUS HEMODYNAMICS
307
TABLE V l . u A i r plethysmography [7-12] Coefficient of variation (%)
Normal limbs
Primary VV*
DVD t
ml
10.8-12.5
100-150
100-350
70-320
sec
8.0-11:5
70-170
5-70
5-20
ml
6.7-9.4
60-150
50-180
8-140
ml
6.2-12
2-45
50-150
60-200
ml/sec
5.3-8
0.5-1.7
2-25
7-30
%
2.9-9.5
60-90
25-70
20-50
%
4.3-8.2
2-35
25-80
30-100
Units Direct measurements
Functional venous volume (VV). (The increase in leg volume on standing) Venous filling time (Time taken to reach 90% of VV) Ejected volume (Decrease in leg volume as a result of one tiptoe maneuver) Residual volume Volume of Blood left in the veins after 10 tiptoe maneuvers Desired movements
Venous filling index (Average filling rate: 90% VV/VFT 90 ~) Ejection fraction = (EV**/VV) • 100 Residual volume fraction - (RVtt/VV) x 100 *VV varicose vein t D V D = deep venous disease w 90 - venous filling time *'EV - ejected volume t t R V - residual volume
TABLE Vll.--Incidence of the sequelae of venous disease in relation to the venous filling index [7-12]
VFI* (ml/sec) 10 *VFI
Chronic swelling (%) 0 12 46 76
Skin changes with/ without Ulceration ulcers (%) (%) 0 0 0 0 46 61 58 76
TABLE IX--Incidence of ulceration in 175 limbs with venous disease in relation to ejection fraction and venous filling index [11]
VFI t < 5 VFI 5-10 VFI > 10
No. 41 37 32
EF* > 40% Incidence of ulceration 2% 30% 41%
No. 19 19 27
EF< 40% Incidence of ulceration 32% 63% 70%
*EF - ejection fraction tVFI - venous filling index
V e n o u s filling index
TABLE Vlll.--Incidence of ulceration in relation to the residual volume fraction of the calf muscle pump in 175 limbs with venous disease [11]
Residual volume fraction (%) < 30 31-40 41-50 51-60 61-80 > 80
Number 20 24 48 43 32 8
Incidence of ulceration (%) 0 8 27 42 72 87
TABLE X.--Arm/foot pressure differential in limbs with outflow obstruction [13]
Grade I. Fully compensated I1. Partially compensated II1. Partially decompensated IV. Fully decompensated *Arm/foot pressure differentia[
P* at rest 6 (often 10-15) >>>4 No further (often15-20) increase
LOWER E X T R E M I T Y VENOUS HEMOD YNAM1CS
308
TABLE Xl.--Maximum venous outflow [14,15]
Obstruction Normal Moderate Severe MVO* strain gauge (1 sec) >45 45-30 40 40-30 5 mmHg
Lower Extremity Venous Hemodynamics G. Belcaro, D. Christopoulos, A.N. Nicolaides, London, England
Chronic venous insufficiency may be the result of outflow obstruction, reflux or a combination of both. The first question the doctor asks is whether obstruction or reflux are present. The second question is where they are anatomically, if present. The third is how much obstruction or reflux exists (Table I). This last question can be answered in terms of hemodynamics. The tables below list the normal and abnormal hemodynamic values for different anatomically defined conditions. Ambulatory venous pressure (Table II) is defined as the lowest pressure during a ten tiptoe exercise. It is the oldest diagnostic quantitative test. Ambulatory venous pressure will be high in the presence of popliteal reflux (Table III). For ambulatory venous pressure from 40 to 80 there is a linear relationship with the incidence of ulceration irrespective of what (obstruction or reflux) and where it is (superficial or deep) (Table IV). Ambulatory venous pressure reflects the net effect of all abnormalities that affect hemodynamics. Photoplethysmographic (PPG) refilling time is similar to ambulatory venous pressure-refilling time. It can identify normal limbs and limbs with superficial and deep venous disease (Table V), However, it is a poor measure of the severity of deep venous disease. Ambulatory venous pressure may be in the range of 45-90 mmHg while the PPG-refilling time is very short (< l0 sec). In this situation a reduction in ambulatory venous pressure (for example, as a result of valve transplantation) will have little effect, if any, on refilling time. From the Irvine Laboratory for Cardiovascular Investigation and Research, Academic Surgical Unit, St. Mary's Hospital Medical School, London, England. Reprint requests: Andrew N. Nicolaides, Irvine Laboratory for Cardiovascular Investigation and Research, Academic Surgical Unit, St. Mary's Hospital Medical School, Praed Street, London W2 1PG, England.
Air-plethysmography provides quantitative information about the various components of the calf muscle pump (Table VI): the amount of blood in the reservoir (venous volume), the stroke volume of single step (ejected volume), the ejection fraction, the amount of reflux in ml/sec (VFI) and finally the residual volume (RV) as a result of t e n tiptoe movement. The residual volume fraction is linearly related to the ambulatory venous pressure and provides an indirect method to measure ambulatory venous pressure noninvasively. Tables VII-IX show the relationship between the air-plethysmographic parameters and the incidence of chronic swelling, skin changes and ulceration. The arm/foot pressure differential (Ap) with needles in arm and foot veins when the patient is horizontal is the most direct method of assessing the severity of outflow obstruction (Table X). The maximum venous outflow (MVO) using strain gauge plethysmography and one second outflow fraction (OF) using air-plethysmography are noninvasive methods of assessing obstruction (Table XI). The relationship between arm/foot pressure differential (Ap) and OF is shown in Table XII. The immediate and long-term effects of elastic compression on venous hemodynamics are shown in Tables XIII and XIV. It appears that graduated elastic compression reduces ambulatory venous pressure by decreasing reflux and increasing the ejection fraction, resulting in a reduced residual volume fraction. The latter is the amount of blood in the calf and determines the ambulatory venous pressure. The improved hemodynamics persist when the compression is removed and the limb retested four weeks later. Venous hypertensive microangiopathy is the result of chronic venous hypertension. It consists of an increased skin blood flow and a reduction in the venoarteriolar reflex. The latter is a physiological vasoconstrictory response to standing, it prevents
305
LOWER EXTREMITY VENOUS HEMOD YNAMICS
306
high pressure and flow in the capillary bed. In the presence of hypertensive microangiopathy, the high flow is associated with an increased capillary permeability and rate of ankle swelling on standing. Transcutaneous PO 2 measurements are related to the number of nutrient capillary loops open and not to overall blood flow (fibrosis and edema tend to obliterate them). However, because of the high diffusion rate of CO2, transcutaneous PCO 2 measurements are related to overall skin blood flow. Therapeutic methods that improve venous hemodynamics and venous hypertension, improve the microcirculation. The measurements shown in Table XV are providing a means of studying and understanding the microcirculation and associated skin changes in the gaiter area of the leg. TABLE I.--Grades of reflux in the deep veins on descending venography [1,2] Grade 0
Grade 1 Grade 2 Grade 3 Grade 4
No reflux below the confluence of the superficial and profunda femoris veins, i.e. the uppermost valve of the superficial femoral vein is competent. Reflux beyond the uppermost valve of the superficial femoral vein but not below the middle of the thigh. Reflux into the superficial femoral vein to the level of the knee. Popliteal valves competent. Reflux to a level just below the knee. Incompetent popliteal valves but competent valves in the axial calf veins. Reflux through the axial veins (femoral, popliteal and calf veins) to the level of the ankle.
ANNALS OF VASCULAR SURGERY
TABLE IIl.--Relationship between venographic grades of reflux in the deep veins, ambulatory venous pressure and refilling time [4]
Grades 0-2 Grades 3-4
AVP* (mmHg) No ankle Ankle cuff cuff
RTgot (sec) No ankle Ankle cuff cuff
30-70 50-95
2-15 1-8
10-45 40-90
13-45 2-14
*AVP = ambulatory venous pressure tRTgo = refilling time
TABLE IV.--The incidence of active or healed ulceration in relation to ambulatory venous pressure in 251 limbs [5] II
P(mmHg)
34 44 51 45 34 28 15
80
Incidence of ulceration (%) 0 12 20 38 57 68 73
TABLE V.--Photoplethysmographic refilling time without and with an ankle cuff to occlude the superficial veins [6] Standing No ankle Ankle cuff cuff Normal SVI t DVI ~
18-80* 5-18 3-12
Sitting No ankle Ankle cuff cuff
18-80 18-50 618"*
26-100 2-25 2-28
26-100 18-50 2-30
*RTgo > 18 sec without cuff identifies normal limbs. tSVI = superficial venous insufficiency ~DVI = deep venous insufficiency **RTgo < 18 sec with cuff identifies limbs with deep venous disease
TABLE II.--Ambulatory venous pressure and refilling time measured with cannulation of the foot vein [3]* AVP t (mmHg) Type of limb Normal Primary varicose veins with competent performating veins Primary varicose veins with incompetent perforating veins Deep venous reflux (incompetent popliteal valves) Popliteal reflux and proximal occlusion Proximal occlusion and competent popliteal valves
No ankle cuff
RTgow (sec) Ankle cuff
No ankle cuff. 18-40 10-18
Ankle cuff
15-30 25-40
15-30 15-30
40-70
25-60**
5-15
8-30**
55-85
50--80
3-15
5-15
60-110
60-120
--
--
25-60
10-60
--
--
*Standard exercise: 10 tiptoe movements tAmbulatory venous pressure w time **In one-third of these limbs AVP remained more than 40 mmHg and RT9o less than 15 seconds despite the application of the ankle cuff.
18-40 18-35
VOLUME 5 N o 3 - 1991
LOWER EXTREMITY VENOUS HEMODYNAMICS
307
TABLE V l . u A i r plethysmography [7-12] Coefficient of variation (%)
Normal limbs
Primary VV*
DVD t
ml
10.8-12.5
100-150
100-350
70-320
sec
8.0-11:5
70-170
5-70
5-20
ml
6.7-9.4
60-150
50-180
8-140
ml
6.2-12
2-45
50-150
60-200
ml/sec
5.3-8
0.5-1.7
2-25
7-30
%
2.9-9.5
60-90
25-70
20-50
%
4.3-8.2
2-35
25-80
30-100
Units Direct measurements
Functional venous volume (VV). (The increase in leg volume on standing) Venous filling time (Time taken to reach 90% of VV) Ejected volume (Decrease in leg volume as a result of one tiptoe maneuver) Residual volume Volume of Blood left in the veins after 10 tiptoe maneuvers Desired movements
Venous filling index (Average filling rate: 90% VV/VFT 90 ~) Ejection fraction = (EV**/VV) • 100 Residual volume fraction - (RVtt/VV) x 100 *VV varicose vein t D V D = deep venous disease w 90 - venous filling time *'EV - ejected volume t t R V - residual volume
TABLE Vll.--Incidence of the sequelae of venous disease in relation to the venous filling index [7-12]
VFI* (ml/sec) 10 *VFI
Chronic swelling (%) 0 12 46 76
Skin changes with/ without Ulceration ulcers (%) (%) 0 0 0 0 46 61 58 76
TABLE IX--Incidence of ulceration in 175 limbs with venous disease in relation to ejection fraction and venous filling index [11]
VFI t < 5 VFI 5-10 VFI > 10
No. 41 37 32
EF* > 40% Incidence of ulceration 2% 30% 41%
No. 19 19 27
EF< 40% Incidence of ulceration 32% 63% 70%
*EF - ejection fraction tVFI - venous filling index
V e n o u s filling index
TABLE Vlll.--Incidence of ulceration in relation to the residual volume fraction of the calf muscle pump in 175 limbs with venous disease [11]
Residual volume fraction (%) < 30 31-40 41-50 51-60 61-80 > 80
Number 20 24 48 43 32 8
Incidence of ulceration (%) 0 8 27 42 72 87
TABLE X.--Arm/foot pressure differential in limbs with outflow obstruction [13]
Grade I. Fully compensated I1. Partially compensated II1. Partially decompensated IV. Fully decompensated *Arm/foot pressure differentia[
P* at rest 6 (often 10-15) >>>4 No further (often15-20) increase
LOWER E X T R E M I T Y VENOUS HEMOD YNAM1CS
308
TABLE Xl.--Maximum venous outflow [14,15]
Obstruction Normal Moderate Severe MVO* strain gauge (1 sec) >45 45-30 40 40-30 5 mmHg
