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Biomedical subjects

I C Roddie

Publications and source records attributed to I C Roddie.

At least 19 recordsLinked to original sources
PubMed1990

The effect of acute changes in blood flow on local lymph flow in the limbs of anesthetized sheep.

A study was made of the effects of acute changes in local blood flow on lymph flow in the feet of anesthetized sheep. Lymph outflow pressure and flow and venous pressure were measured in cannulated vessels draining the foot region. Local volume changes were also measured. Acute reductions in blood flow were produced by sudden occlusion of the circulation to the limbs with a pneumatic cuff for periods of up to 1.5 hours. During the first 10 min of occlusion, there was little change reaching about 25% of its control value after 40 min of arrest. On release of the circulation, lymph flow rose almost immediately to levels above the control value, resulting in a hyperlymphia whose size and duration was related to the duration of the circulatory arrest and the limb volume changes that followed. The results indicated that lymph flow can continue, albeit at reduced rates for long periods after circulatory arrest and that during reactive hyperaemia, there is a brisk hyperlymphia whose size and time course is similar to that of the limb volume changes.

Anesthesia, General↗
PubMed1989

Lymph flow in sheep limbs during local exposure to subatmospheric pressure.

1. Lymph flow and pressure were measured via cannulae inserted into afferent lymphatics draining the feet of anaesthetized sheep. 2. When the cannula outlet was at limb level, local exposure of the limb to graded decreases in ambient pressure caused graded increases in lymph flow with pressure values down to -50 mmHg. 3. When the cannula outlet was lowered below limb level to offset the negative pressure gradient imposed on the lymphatic vessels by suction, lymph flow rose progressively with decreasing ambient pressure values down to -70 mmHg. 4. When negative pressure gradients were imposed on the lymphatic vessels by raising the lymphatic cannula outlet in progressive steps above limb level, the vessels were able to expel lymph against gradients of up to 50 mmHg but lymph flow was greatly reduced against a gradient of 70 mmHg. 5. The results suggest that subatmospheric pressure may affect local lymph flow in two ways. By increasing blood capillary transmural pressure it may increase lymph flow by increasing tissue fluid formation. By imposing a negative pressure gradient along the lymphatics it may decrease lymph flow, especially at the most negative pressures, and the lymph flow response to subatmospheric pressure may be the algebraic sum of both effects.

Animals↗
PubMed1987

Peripheral lymphatic responses to outflow pressure in anaesthetized sheep.

1. Lymph flow and pressure fluctuations were measured by cannulating popliteal efferent and distal hind-limb afferent lymphatic vessels in anaesthetized sheep. The cannula outflow height was raised above the vessels to increase lymphatic outflow pressure. 2. Lymph flow decreased non-linearly as the outflow was raised. The rate of decrease increased with increasing outflow height. 3. Lymphatic contraction frequency rose and stroke volume fell with increasing outflow height. 4. The calculated power necessary to move lymph along the cannula initially increased with outflow height but it reached a peak and was reduced again by raising the outflow further. Calculated lymphatic stroke work followed a very similar pattern. 5. Lymph flow was maintained up to a greater outflow height in afferent than in efferent vessels. Curves relating frequency, power and stroke work to outflow height were shifted to the right in the afferent lymphatics. 6. These results are consistent with an intrinsic lymphatic pump which can be stimulated by increasing pressure. At high pressures, however, the pump fails.

Animals↗
PubMed1987

Comparison of fluid transport systems in lymphatics and veins.

In the anesthetized sheep, pressure pulses generated in the feet are transmitted downstream in the veins but not in the lymphatics at normal intralymphatic pressure. When the sheep is tilted on a tilt table, gravitational changes occur in venous pressure but not in the pressure in adjacent lymphatics. These results suggest that in limb lymphatics, unlike limb veins, the column of fluid is incomplete. This makes extrinsic pumping less effective for propelling fluid in lymphatics than in veins. At normal intralymphatic pressures, intrinsic pumping seems to be mainly responsible for lymph propulsion. The incompleteness of the fluid column in lymphatics might also protect these vessels against the hydrostatic problems experienced by veins during gravitational stress.

Animals↗
PubMed1987

Resistance in the sheep's lymphatic system.

Saline was infused in a downstream direction into the afferent lymphatics in the metacarpal region of anesthetized sheep. The changes in inflow pressure were measured over 10 min periods with flow rates ranging from 10-2000 microliters/min. Flow rates in the physiological range generated mean pressures of about 30 mmHg and flows of 1 ml/min generated mean pressures of about 60 mmHg. Resistance was relatively high at flow rates in the range of 10-15 microliters/min but sharply decreased above that and was relatively constant at flows greater than 500 microliters/min. Adding isoprenaline (1 microgram/min) to the infusate reduced spontaneous contractile behavior in the infused system and lowered the resistance at the lower flow rates. It is concluded that the peripheral lymphatic system in the sheep offers substantial resistance to lymph flow and that substantial intralymphatic pressure is needed to return lymph from the periphery especially at higher flow rates.

Animals↗
PubMed1986

Measurement of capillary pressure in humans using a venous occlusion method.

The venous occlusion technique was used to measure capillary pressure in the forearm and foot of man over a wide range of venous pressures. In six recumbent subjects venous pressure (Pv) in the forearm (mean +/- SE) was 9.3 +/- 1.4 mmHg and the venous occlusion estimate of capillary pressure (Pc) was 17.0 +/- 1.6 mmHg, whereas in another six subjects Pv in the foot was 17.1 +/- 1.2 mmHg and Pc was 23.4 +/- 2.5 mmHg. Venous pressure in the limbs was increased either by changes in posture or by venous congestion with a sphygmomanometer cuff. On standing Pv in the foot increased to 95.2 +/- 1.5 mmHg and Pc rose to 112.8 +/- 3.1 mmHg. The relationship established between venous pressure and capillary pressure in the forearm is Pc = 1.16 Pv + 8.1, whereas in the foot the relationship is Pc = 1.2 Pv + 1.6. The magnitude and duration of the changes in capillary pressure were also recorded during reactive hyperemia. The venous occlusion method of measuring capillary pressure is simple and easily applied to studies in humans.

Blood Pressure↗
PubMed1976

Venous distensibility during pregnancy determined by graded venous congestion.

The increase in volume of the human calf and forearm during pregnancy resulting from graded venous congestion has been measured plethysmographically in the raised leg and forearm of 10 recumbent subjects during and after pregnancy. Normal pressure volume curves were determined and the alterations in this curve over the various stages of gestation were presumed to indicate an alteration in the distensibility of the capacity blood vessels. This distensibility was found to increase with the progression of pregnancy in both the forearm and the calf particularly after the thirtieth week of pregnancy. The distensibility, however, appeared to return to below the 10 week gestation level at the eighth postpartum week. The increase in distensibility was greater in the calf than in the forearm although both were significantly increased.

Adult↗
PubMed1976

The effect of transmural pressure on pumping activity in isolated bovine lymphatic vessels.

1. Isolated preparations of bovine mesenteric lymphatics containing about seven valved segments were cannulated and set up in a perfusion system so that, when the preparation was not contracting, the inflow and outflow pressures were exactly equal and there was no flow through the preparation. 2. Transmural pressure was varied by raising or lowering the inflow and outflow pressures simultaneously by the same amount. 3. The isolated vessels showed rhythmic spontaneous activity; it consisted of quick contractions which spread rapidly over the entire preparation, each followed by a rapid relaxation and a diastolic pause. 4. With each contraction, the preparation decreased in both length and diameter and generated an outflow pressure which pumped fluid in the direction determined by the orientation of the values. 5. Raising the transmural pressure in the preparation increased the output of the preparation; this was achieved by an increase in both the frequency and force of the individual contractions. 6. It was concluded that bovine lymphatics could propel fluid by their intrinsic activity at a rate which was related to the degree of distension of their walls.

Animals↗