摘要:

The production of constrictive responses limited to either arterial or venous segments of the vasculature of the dog paw was tested by stimulating various peripheral nerves of the hind leg. Resistance changes of the total vasculature of the paw, and of three of its component series-coupled segments (arterial, small vessel, and venous) were studied sequentially before and during stimulation of the sciatic nerve and of three of its branches (tibial, deep, and superficial fibular nerves). Stimulation characteristics (15 to 90 volts, 1-3 msec duration, 25/sec, and 30-second stimulation periods) were chosen to produce maximum vasoconstrictive responses. Tibial and deep fibular nerve stimulations produced constriction of the arterial segment but not of the venous segment. Superficial fibular nerve stimulation produced constriction of the venous segment but not of the arterial segment. All nerve stimulations produced constriction of small blood vessel segments. Thus, responses could be limited to either arterial (plus small vessel) or venous (plus small vessel) segments. Inability to localize response within small-vessel segments made it impossible to determine whether any peripheral nerve produced constrictive responses limited strictly to either pre- or postcapillary segments. No relationship was evident between control resistance values and the subsequent changes in resistance occurring in response to the standard stimulations.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

A horizontal isolated lung preparation has been used to examine the transmission of pulsatile blood pressure and flow. Arterial and venous pressure and flows were measured with pressure transducers and electromagnetic flowmeters. After a sudden increase in pulmonary arterial pressure, delays of several seconds were observed before venous flow began to increase. Flow then increased slowly over a period of 1 to 9 seconds to a new steady level. The transmission of pulsatile flow was independent of the outlet pressure and identical for perfusion in the forward and reverse directions. Flow transmission fell from about 75% at a frequency of 0.03 cps to approximately 10% at a frequency of 1 cps. Pressure transmission down to the collapsible vessels was measured when alveolar pressure exceeded venous pressure. At 0.1 cps approximately 50% of the incident pressure wave was transmitted, and at 1 cps this was reduced to 30%. It was concluded that the lung passed well only the low-frequency components of the applied input and that in a vertical lung only about 30% of the mean to peak pressure pulse would be transmitted down to the small vessels and therefore affect the distribution of blood flow.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The sympathetic innervation of the rabbit heart, as a function of age, was studied by measuring the cardiac concentration of catecholamines and observing the anatomic distribution of sympathetic nerves by the monoamine fluorescense technique. The cardiac concentration of norepinephrine in late gestation was quite low; the levels rose progressively after birth to reach adult levels by about three weeks of age. Similar small amounts of epinephrine were found in the hearts at all ages. Substantially less change in adrenal catecholamines accompanied advancing age. At all ages a close correlation was noted between the norepinephrine levels and the histochemical demonstration of sympathetic innervation. Intensely fluorescent, terminal varicosities were observed within large preterminal nerve trunks only in the youngest animals, suggesting that the sympathetic nerves move into, rather than form within, the heart. Chromaffin cells were observed in the hearts at all ages.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The effects on myocardial oxygen consumption and mechanics of acute, simulated aortic and mitral regurgitation were studied in open-chest, anesthetized dogs to determine how changes in the mechanical performance of the ventricle alter oxygen consumption. When regurgitation was induced acutely with effective stroke volume (total stroke volume less regurgitant volume) and heart rate held constant, left ventricular end-diastolic volume, total stroke volume, the ejection fraction, left ventricular wall tension, and the extent of shortening of the contractile element and the circumferential fibers all increased. With volumes of regurgitation approaching effective systemic blood flow, oxygen consumption increased only moderately, despite the increases in tension and shortening. When valvular regurgitation was induced while peak ventricular wall tension was held relatively constant, stroke volume doubled and the extent of both contractile element and circumferential fiber shortening increased. Contractile element work in generating tension was unchanged; that which led to fiber shortening increased substantially. Myocardial oxygen consumption did not increase significantly. Thus, marked increases in the efficiency of the contractile elements and myocardial fibers occurred. The low energy cost per unit of work expended in shortening as opposed to that used for tension development therefore allows the excess stroke volume of valvular regurgitation to be maintained at only a small added oxygen cost to the ventricle.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The effect of exercise on the vasoconstrictive response to sympathetic stimulation was studied by observing the changes in perfusion pressure in dogs' hindlimbs perfused at constant flow. During steady-state simulated exercise, a time-dependent increase occurred between 10 and 30 minutes in the magnitude of response to lumbar trunk stimulation or carotid sinus hypotension. This was present (although to a reduced Degrees) in drug-induced vasodilatation and in exercising limbs perfused at constant pressure. The time-dependent change was not due to (1) repetition of stimulus, (2) artifact from muscle electrodes, (3) circulating vasoactive substances, (4) skin circulation, or (5) pH, PCO2, or temperature of the perfusing blood. When norepinephrine was used as the vasoconstrictive stimulus, no time-dependent change was noted. After stabilization, the frequency-response curve of exercising muscle exceeded that at rest at all blood concentrations of norepinephrine and at all save the lowest frequencies of stimulation. It was concluded that vascular smooth muscle can develop greater tension from greater initial length. However, during exercise some factor which operates between the sympathetic nerve ending and the receptor site on vascular smooth muscle initially tends to depress this enhanced ability to develop tension.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The assumption of incompressibility has often been applied to the analysis of arterial-wall elasticity; however, the supporting evidence has been incomplete. The present study was designed to explore this problem in greater depth by accurately measuring the changes in tissue volume associated with large, induced strains on 11 thoracic aorta segments excised from dogs. The radial, circumferential, and longitudinal stresses were measured as the artery was subjected to an internal pressure and longitudinal stretch greater than those in vivo. From these data it was possible to calculate the hydrostatic stress. The associated changes in volume of the aortic wall tissue were measured with a specially designed apparatus. The greatest volumetric strain (ΔV/V) was 0.00165. The bulk moduli obtained by dividing the hydrostatic stresses by the corresponding volume strains averaged 4.44 × 106g/cm2. Similar studies were also carried out on the abdominal aorta and the carotid, iliac, and pulmonary arteries. The volumetric strains observed were of the same magnitude. It is concluded that for most practical purposes arteries may be considered incompressible.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The electrical threshold of A-V nodal cells of isolated rabbit heart preparations was estimated by techniques which permitted stimulation and recording through the same micropipette. Cells within the node were significantly less excitable than adjacent atrial and ventricular tissues; thresholds exceeded 5 × 10-6amp in some instances. Recovery of excitability was delayed well beyond repolarization; in cells of the midnodal region, “diastolic” threshold was not attained until 0.2 to 0.5 seconds after restoration of resting membrane potential. A cumulative effect of frequency upon excitability (fatigue) was demonstrated. At high driving rates, the lag in recovery was further delayed, and the late diastolic threshold was increased. Responses to single-cell stimulation indicate that summation may be an important feature of propagation within the node.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID