Arterial pressure was measured simultaneously in the thumb and in the contralateral arm using strain-gauge plethysmography in 100 healthy persons aged 13--43 yr, before and after compression of the radial or the ulnar artery. The radial and ulnar pulses were palpable in all instances. In 29 (14.5%) hands compression of either artery did not reduce the thumb pressure. In 152 (76%) occlusion of the radial artery caused a decrease of more than 10 mm Hg, but never to less than 40 mm Hg. In 91 (45.5%) occlusion of the ulnar artery reduced thumb pressure, on three occasions to less than 40 mm Hg. Radial dominance was shown in 110 hands (55.0%), 24 (12.0%) showed ulnar dominance and in 66 (33.0%) neither vessel dominated.

Blood flow and filtration of water across the vascular bed in human forearm muscles were studied at rest and during graded exercise with a hand ergometer. Blood flow was measured by dye dilution and water filtration was determined after injection of hyperoncotic albumin solution (23%) in the brachial artery creating a tissue to blood ultrafiltration measureable as a dilution in the effluent blood. The filtration constants were expressed as a filtration coefficient Fc (ml water/ml plasma mmHg increase in oncotic pressure), and, multiplying by the plasma flow, as a filtration capacity Kf (ml water/100 ml tissue min mmHg increase in oncotic pressure). During the increase in plasma flow induced by exercise, Fc remained constant at about 0.0007, but Kf increased in parallel with the hyperaemia from 0.0031 to 0.038 when plasma flow increased from 4 to 48 ml (100 ml min)-1. The data suggest a more massive recruitment of exchange area during exercise (a factor 12) than suspected on the basis of ultrafiltration in animals made with the prolonged venous stasis technique (showing a factor 2-5). The estimated variability in exchange surface area indicates, that animal studies of muscle circulation, whether pertaining to capillary permeability or capillary filtration should gain by an independent estimate of the number of capillaries that are flowing during the particular experimental situation.

Water filtration in the human forearm was determined with a new method using a hyperoncotic transient of albumin solution infused into the brachial artery. Baseline dilution of labelled albumin in deep forearm vein plasma in excess of the contribution from arterial blood and from infusate was assumed to originate from extravascular water filtered into the blood by the transient. The filtration coefficient (Fc) was determined as the ratio between filtered water and increase in colloid osmotic pressure in the blood samples, and gives the filtrative water permeability in the exchange areas of the microcirculation. In 10 normal volunteers, Fc was 0.00082 ml (ml mmHg)-1 (SD=0.00007). Multiplication of Fc by plasma flow in the forearm gave a filtration capacity (Kf) of 0.0036 ml (100 ml tissue min mmHg)-1 (SD=0.00137). This filtration capacity (Kf) represents that of fast flowing regions in the forearm muscles, but it is of the same order of magnitude as the capillary filtration coefficient (CFC) determined plethysmographically for the entire forearm by the venous stasis technique.

Reports of sudden death of patients during i.v. administration of methylprednisolone (M.P.) prompted the present study of the hemodynamic effect of M.P. given i.v. to dogs. Fifteen healthy, mongrel dogs were anesthetized with thiomebumal, fentanyl, droperidol, pancuronium and N2O/O2. With ventilation and circulation in steady state, M.P. 30 mg/kg b.w. was given i.v. either as a push bolus (n=7) or over a 5-min period (n=8). In the bolus group, mean aortic pressure (MAP) and systemic vascular resistance (SVR) had decreased to 72 and 60%, respectively, 1 min after the start of the steroid injection, while heart rate (HR), cardiac index (CI), mean pulmonary arterial pressure (MPAP) and left ventricular work (LVW) had not changed significantly. In the 5-min group, the HR increased by 23%, while the other parameters were unchanged during the injection period. Within 5 min after the termination of the steroid injection all hemodynamic parameters had returned to pre-injection levels in both groups. Sodium, potassium, magnesium, protein and calcium in serum were unchanged in both groups during the injection period and in the following 15 min. A significant, transient fall in ionized calcium was observed in all six dogs in which this ion was measured. It was concluded that rapid i.v. injection of pharmacological doses of M.P. in hemodynamically stable, anesthetized dogs causes immediate, transient decreases in SVR and MAP. The mechanisms may be an alpha adrenergic blocking action or a direct effect on the muscles in the peripheral vessels, combined with a negative inotropic effect on the myocardium, possibly mediated through an impeded calcium release.

Blood pressure was measured in both great toes using strain-gauge plethysmography in 100 healthy persons aged 18 to 43 before and during successive compression of the dorsalis pedis artery, the posterior tibial artery, and both arteries at the same time. In 54 (27 percent) of 200 feet, successive compression of the dorsalis pedis and the posterior tibial arteries produced no decrease in pressure in the great toe. In 47 of the feet, toe pressure decreased significantly only after compression of the posterior tibial artery, and in 65 of the feet toe pressure decreased significantly only after compression of the dorsalis pedis artery. In 34 of the feet, toe pressure decreased significantly after compression of each of the arteries. Thus in 99 (50 percent) of 200 feet, compression of the dorsalis pedis artery decreased the pressure in the great toe significantly, and in 4 feet the pressure decreased below 40 mm Hg. When both arteries were simultaneously compressed, 69 feet showed detectable blood pressure in the great toe. Attempts to evaluate adequacy of collateral circulation by pressure blanching of the great toe prior to artery compression and then observing capillary refilling time upon release of toe compression proved unreliable.