Reactions of the blood vessels of the human forearm to increases in transmural pressure

Abstract

Bayliss showed in 1902 that a sudden rise of arterial pressure causes the volume of the hindlimb of dogs, cats and rabbits to decrease below the original after a preliminary increase. The response was unaltered by acute denervation. He also found that arrest of the circulation to a curarized hindlimb for as little as 2 sec was followed by a large increase in the volume of the limb. These effects he ascribed to a direct reaction on the part of the muscular walls of the arteries, an increase in pressure causing constriction and a decrease dilatation. This explanation has been criticized by many workers, but has recently received support. Folkow (1949) has measured directly the arterial perfusion pressure in, and the rate of venous outflow from, the hindlimbs of anaesthetized cats. Very short (5 sec) periods of interrupted arterial inflow were followed by a pronounced vasodilatation which was substantially the same in the normal, acutely and chronically sympathectomized and chronically de-afferented limb respectively. In the acutely sympathectomized limb, a partial arterial occlusion, sufficient to lower the perfusion pressure, but not sufficient to lower the rate of blood flow below that occurring before sympathectomy, was also followed by vasodilatation. The dilatation following partial arterial occlusion was unaltered by large variations in the oxygen and carbon dioxide percentages in the inspired air. Sudden steps up or down in the arterial perfusion pressure of the acutely denervated hindlimb of the cat (Folkow, 1953) caused sudden rises and falls respectively in the rate of venous outflow; in all cases, however, the rate of venous outflow gradually returned over the next minute towards, but not to, its original level. These observations support the view that the resistance vessels respond by dilatation to a fall and by constriction to a rise of perfusing pressure, although it is not clear whether the mean or the pulsatile pressure constitutes the predominant stimulus. Hilton's (1953) observation that the outflow from the cat's hindlimb is increased after arterial occlusion but not after venous occlusion gives further support.

Vacuum therapy in erectile dysfunction—science and clinical evidence

“…80 There has been growing evidence to support this. Blair et al 81 documented that sub-atmospheric pressure induces an initial increase in arterial inflow in the forearm of healthy volunteers; Greenfield and Paterson 82 further showed a vasodilation effect on the arteries of the forearm in volunteers exposed to a subatmospheric pressure of À150 to À200 mm Hg, which is similar to the pressure used in VED. 14 Diederichs et al 83 noticed that negative pressure induces expansion of penile tissue followed by increase in blood flow in primates; the authors believed that the increased blood flow was arterial inflow.…”

Angiotensin converting enzyme inhibition does not affect the response to exogenous angiotensin II in the human forearm.

“…When responses were expressed as the percentage change in forearm blood flow (Figure 1) to correct for possible changes caused by extraneous factors such as altered level of arousal [16], the conclusion that The mean (± s.e. mean) baseline angiotensin II level was 7.88 ± 1.1 pg ml-' (normal range 5-35 pg ml-') which did not differ significantly from placebo 7.4 ± 1.7 pg ml-'.…”

The effects of 7-hour local hyperglycaemia on forearm macro and microcirculatory blood flow and vascular reactivity in healthy man

“…This calculated ratio corrects for all systemic factors that affect the regulation of blood flow in both arms (e. g. changes in blood pressure, level of arousal, hormonal changes etc. ), and ensures that only the direct effects of locally infused substances on forearm blood flow are taken into account [18]. In an earlier study on diurnal variations of forearm macro and microeirculation, the FBF ratio was demonstrated to be stable during the day [19].…”