Comparison of direct and indirect blood pressure measurement in anesthetized dogs.

This study was conducted to determine whether blood pressures and pulse rate could be determined accurately by indirect measurements from the front and hind legs of 15- to 40-kg dogs anesthetized with isoflurane. Indirect measurements from each animal were compared to direct measurements obtained from a catheter placed into the abdominal aorta via the femoral artery at four ranges of systolic pressure. When systolic pressure was above 80 mm Hg, indirect measurements were either the same as direct measurements or slightly lower. However, when systolic pressures were below 80 mm Hg, indirect systolic pressure measurements were 6 to 15% higher than direct measurements. Larger differences in diastolic pressures were found, which resulted in differences in mean pressure. The most accurate measurements were found when the cuff width-to-limb circumference ratio was between 0.4 and 0.6 and when systolic pressure was between 80 and 100 mm Hg.     

Simultaneous pressure and 19F NMR pH measurements of smooth muscle cells of intact hog carotid arteries at rest and during contractions with norepinephrine

Using 19F NMR we have measured the intracellular pH of the vascular smooth muscle cells of hog carotid arteries at rest and during contractions induced with norepinephrine. Experiments were performed on single, intact arteries closed at both ends, superfused from the lumen and loaded with the 19F NMR pH indicator alpha-difluoromethylalanine. At rest, luminal pressure was maintained at 100 +/- 2 mm Hg and intracellular pH was 7.12 +/- 0.04. Contractions elicited with 10(-5) M norepinephrine were associated with a pressure increase of 18 +/- 6 mm Hg and a decrease in pH of 0.04 +/- 0.02 units.     

Cryo-electron microscopy analysis of myosin at work and at rest

Myosins are a superfamily of ATP-driven actin-dependent molecular motors that are responsible for diverse functions from muscle contraction to cell division. The resolution revolution in cryo-EM has enabled characterisation of the interaction of myosin with its actin track in several states of the myosin motor cycle, for multiple myosin classes, allowing increased insight into the force generation mechanism. A major advancement in our understanding of myosin-2 regulation has come through solving structures of its shutdown state, dysregulation of which is implicated in multiple diseases. This review will discuss what has been accomplished so far with cryoEM, what is still yet to do, but within reach, and how better understanding of myosin structure–function relationships may lead to future therapeutic interventions.     

Comparison of direct and indirect measurements of pulmonary capillary transit times

Using in vivo microscopy, we made direct measurements of pulmonary capillary transit time by determining the time required for fluorescent dye to pass from an arteriole to a venule on the dependent surface of the dog lung. Concurrently, in the same animals, pulmonary capillary transit time was measured indirectly in the entire lung using the diffusing capacity method (capillary blood volume divided by cardiac output). Transit times by each method were the same in a group of five dogs [direct: 1.75 +/- 0.27 (SE) s; indirect: 1.85 +/- 0.33 s; P = 0.7]. The similarity of these transit times is important, because the widely used indirect determinations based on diffusing capacity are now shown to coincide with direct measurements and also because it demonstrates that measurements of capillary transit times on the surface of the dependent lung bear a useful relationship to measurements on the capillaries in the rest of the lung.     

Direct and indirect measurements of Phloem turgor pressure in white ash

Direct determinations and indirect calculations of phloem turgor pressure were compared in white ash (Fraxinus americana L.). Direct measurements of trunk phloem turgor were made using a modified Hammel-type phloem needle connected to a pressure transducer. Turgor at the site of the direct measurements was calculated from the osmotic potential of the phloem sap and from the water potential of the xylem. It was assumed that the water potentials of the phloem and xylem were close to equilibrium at any one trunk location, at least under certain conditions. The water potential of the xylem was determined from the osmotic potential of xylem sap and from the xylem tension of previously bagged leaves, measured with a pressure chamber. The xylem tension of bagged leaves on a branch adjacent to the site of the direct measurements was considered equivalent to the xylem tension of the trunk at that point. While both the direct and indirect measurements of phloem turgor showed clear diurnal changes, the directly measured pressures were consistently lower than the calculated values. It is not clear at present whether the discrepancy between the two values lies primarily in the calculated or in the measured pressures, and thus, the results from both methods as described here must be regarded as estimates of true phloem turgor.     

Auscultatory indirect measurement of blood pressure in dogs

An indirect method of measuring blood pressure (cuff plus stethoscope) was evaluated in 70 dogs weighing 15 to 30 kg (17.5 +/- 8.8 kg; mean +/- standard deviation). A cuff 12 cm wide was used. The measurements were most audible with the cuff on the upper foreleg of the dog and with the stethoscope placed in the medial epicondylar region just distal to the cuff. The cuff was inflated to greater than systolic pressure and allowed to deflate slowly. In 70 lightly sedated dogs, systolic blood pressures averaged 145 +/- 25 mmHg (mean +/- standard deviation) and diastolic blood pressures averaged 84 +/- 14 mmHg. Indirect measurements were compared to direct measurements (femoral arterial catheter). Systolic pressures obtained by this direct method averaged 138 +/- 29 mmHg (mean +/- standard deviation) and diastolic pressures averaged 84 +/- 17 mmHg. The correlation coefficient for systolic pressure was 0.96 and for diastolic pressure 0.97.     

Reduction of blood pressure by indirect biofeedback

Forty-five randomly assigned subjects served in either a relaxation control, an EMG plus thermal, or a thermal biofeedback group. All groups received the same relaxation manipulation. Experimental results demonstrated a significant drop in both diastolic and systolic blood pressure for the feedback treatment. Diastolic measures showed a somewhat greater decrease for the EMG plus thermal treatment condition. A learning effect was demonstrated both within and across the three experimental sessions. Given that the sample was normotensive, the 20% reduction in blood pressure was notable. The results support the idea that blood pressure biofeedback is not a necessary condition for reduction of arterial blood pressure.