Calf blood flow and posture: Doppler ultrasound measurements during and after exercise.

To investigate the joint effects of body posture and calf muscle pump, the calf blood flow of eight healthy volunteers was measured with pulsed Doppler equipment during and after 3 min of rhythmic exercise on a calf ergometer in the supine, sitting, and standing postures. Muscle contractions seriously impeded calf blood flow. Consequently, blood flow occurred mainly between contractions and reached a plateau that lasted at least the final 100 s of each exercise series. After exercise the blood flow decreased much faster in the sitting and standing postures than in the supine posture. There was no difference in blood flow between various postures during the same submaximal exercise. However, subjects in the standing posture were able to perform exercise with a higher load than in the supine posture, and blood flow in the standing posture could become twice as high as in the supine posture. We conclude that calf blood flow is regulated according to needs; available perfusion pressure determined maximal blood flow and exercise; and compared with the supine posture, the standing posture and calf muscle pump increase the perfusion pressure.

Calf blood flow and posture: Doppler ultrasound calibrated by plethysmography.

A procedure was developed that enables measurement of rapid variations in calf blood flow during voluntary rhythmic contraction of the calf muscles in supine, sitting, and standing positions. During the exercise, maximum blood velocity is measured by Doppler ultrasound equipment in the popliteal artery. The Doppler signals are calibrated by plethysmography to enable calculation of blood flow during exercise in ml.100 ml-1.min-1. Knowledge of the cross-sectional area of the vessel and the angle of insonation is not required in this procedure. Evaluation of the calibration method with 10 healthy volunteers showed that for each subject a new calibration was necessary after a change in posture; the relationship between the blood flow and the maximum Doppler frequency averaged over one heart cycle was linear for each calibration.

Multipurpose ergometer for static and dynamic exercise of the calf muscles.

A calf ergometer is presented that can be used for both static and dynamic exercise in supine, sitting or standing position. During exercise each foot is fixed firmly to a pedal. During dynamic exercise the foot pedal can rotate through an angle which can be varied from 5 to 30 degrees. External work is performed only during plantar flexion. The amount of work is determined by the moment imposed to the pedal by a constant force spring and can be calculated from electrical signals that represent the angle of rotation and the moment exerted to the pedal. During static exercise the foot pedal is secured so that it cannot move.

Maximal blood flow after exercise in patients with intermittent claudication and in normal controls.

In some patients with intermittent claudication blood flow to the calf muscles after exercise was in the same range as in normals. The blood pressure was lower in all patients. The hypothesis is formulated that for these high flow patients the claudication is a result of non-uniform perfusion of the calf muscles.

The effect of six months intensive physical training on the circulation in the legs of patients with intermittend claudication.

Out of 94 patients with intermittent claudication 65 completed a program of 6 months intensive physical training. Every 2 months the blood pressure indices at the thigh and at the ankle and the blood flow in the calf were measured at rest, after 5 min arterial occlusion and after exercise of the calf muscles until claudication. First the reproducibility of the blood pressure indices and the blood flow values was established. An increase of 15 in the pressure indices was considered to be substantial. An increase of 6.0 ml/100 ml/min in flow values was considered a substantial change. The blood pressure indices did not increase significantly during the training period, the blood flow values increased significantly. On the basis of the non-invasive tests no reliable statement can be made as to the expected result of the training.

Changes of walking distance in patients with intermittent claudication during six months intensive physical training.

Patients with intermittent claudication were treated with six months intensive physical training. They were instructed to walk with a speed of 6 km/h until they got complaints and then to rest for some time. This sequence was repeated until men below 65 years had walked 2 km. Men above the age of 65 years and women had to walk 1.5 km. This training session was performed 3 times a day. Every two months the claudication distances in a corridor and on a treadmill were measured. Out of 95 patients 65 completed the training. In 38 patients (59%) there was no substantial change in walking distance. Fourteen patients (22%) doubled their walking distance, seven (11%) could walk more than 1000 m, but their complaints remained. Six (9%) could walk more than 1000 m without claudication pain. Most patients gained their result during the last 2 months of the program. After the training 48% of the patients were satisfied with their walking distance.

Venous capacity, venous refill time and the effectiveness of the calf muscle pump in normal subjects.

With strain gauge plethysmography various procedures to assess the competence of the venous system in the lower leg were compared in 10 normal subjects. The reproducibility and ease of use were established, and normal values were obtained. It is concluded, that measurements in the sitting position are preferable to those in the standing position. To measure the venous capacity, the dependency test is the method of choice. Rhythmic exercise to assess the effectiveness of the calf muscle pump can be restricted to five successive contractions. The refill time after exercise is not a suitable parameter to assess the competence of the venous valves.

Arterial blood pressure and the flow in the calf at rest and during reactive hyperemia.

The influence of a handgrip-induced rise in arterial blood pressure on the blood flow in the calf at rest and on the maximal flow during reactive hyperemia after 5-minute arterial occlusion was studied in 7 healthy subjects. Isometric contractions of the forearm muscles (handgrip) with 20% of the maximal voluntary contraction during 3 minutes caused a significant increase in mean blood pressure of 19% (SEM 3%; p less than 0.05). No significant increase in the mean blood flow at rest was found. The maximal blood flow during reactive hyperemia was increased by 42% (SEM, 5%; p less than 0.05). The lowest peripheral resistance during reactive hyperemia was decreased by 15% (SEM 6%; p less than 0.05).

A continuous wave Doppler velocimeter for monitoring blood flow in the popliteal artery, compared with venous occlusion plethysmography of the calf.

A transcutaneous Doppler velocimeter has been used for monitoring changes in blood flow in the popliteal artery during and after exercise of the calf muscles on a calf-ergometer. The instrument and the positioning of the probe are described. The validity of the Doppler measurements has been assessed by comparing results after exercise and after 5 min arterial occlusion with venous occlusion plethysmography. For 10 healthy volunteers calibration lines were found which are curved. This can be ascribed partly to alinearity of the Doppler instrument and partly to changes of the diameter of the popliteal artery. Displacement of the probe with respect to the artery, which influences the measured velocity signal, can be detected and to a certain extent corrected by taking into account the intensity of the Doppler signal. The largest deviation of a data point from the corresponding calibration line varies for the ten subjects between 90 and 170 Hz in the high flow range (mean Doppler frequency around 1000 Hz) and between 20 and 60 Hz in the low flow range (mean Doppler frequency below 200 Hz).

Venous pressure-volume relation and calf blood flow determined by changes in posture.

The volume capacity of the venous system in the calves of 70 normal subjects was determined by passive and active changes in posture, using mercury-in-rubber strain gauges. The mean volume capacity was 1.26% (SD 0.39%) at a venous pressure of 0 kPa (o mm Hg) and 2.05% (SD 0.70%) at 1.60 kPa (12 mm Hg). With this method the blood flow in the calves at rest was measured without venous occlusion: 2.84 ml-100 ml-1/min (SD 1.20). During interpolated venous occlusion the mean blood flow was 2.67 ml-100 ml-1/min (SD 1.21). The pressure-volume relation over the pressure range 0 to 9.31 kPa (0 to 70 mm Hg) was determined in seven normal subjects.