Effect of increased acceleration on lung expansion in dogs: prone vs. supine body positions.
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Acceleration↗
Biomedical subjects
C F Knapp
Publications and source records attributed to C F Knapp.
Endurance training in dogs increases vascular responsiveness to an alpha 1-agonist.
The effects of endurance training on vascular responsiveness to an alpha 1-agonist and the associated changes in baroreflex modulation of heart rate and vascular resistance were studied. Graded dosages of phenylephrine were given to eight treadmill-trained dogs and to eight untrained dogs; both groups were chronically instrumented and were sedated and resting when tested. These dosages were repeated after ganglionic blockade. Aortic pressure, cardiac output, central venous pressure, peripheral resistance, and heart rate were each averaged over 30 s before injection and 90 s after injection. The slope of the peripheral resistance-dose relationship was significantly increased in trained compared with untrained dogs in both the unblocked and blocked cases [unblocked: trained 0.89, untrained 0.47; blocked: trained 4.30, untrained 2.05 (mmHg.l-1.min)/(microgram.kg-1)]. The unblocked resistance slopes were reduced with respect to the blocked slopes by 77 (untrained) and 79% (trained). The slope of the heart rate-aortic pressure response was reduced, but not significantly, by endurance training. We conclude that 6 wk of endurance training in dogs resulted in a doubling of the vascular responsiveness to an alpha 1-agonist, with no significant change in the baroreflex regulation of resistance or heart rate.
Animals↗
Control of left ventricular function during acceleration-induced blood volume shifts.
Peripheral pooling of blood was produced in chronically instrumented, sedated dogs (n = 7) by subjecting them to a +2 Gz force (along their spinal axis) for 3 min. The acceleratory force was then quickly removed, thereby mobilizing blood toward the thoracic cavity. Left ventricular volume, calculated from ultrasound measurements of major and minor axes and wall thickness, increased (p less than 0.05) from 21.7 +/- 3.6 ml (diastolic, mean +/- S.E.M.) and 14.1 +/- 3.3 ml (systolic) during the peripheral pooling of blood to 28.2 +/- 4.1 ml (diastolic) and 16.0 +/- 2.9 ml (systolic) as measured at 2 min after release of the acceleratory force. The d(LVP)/dt was essentially unchanged (i.e., from 3415 +/- 482 mm Hg.s-1 to 3536 +/- 249 mm Hg.s-1). The experiment was repeated after total pharmacologic autonomic blockade (propranolol, atropine, phenoxybenzamine). Left ventricular volumes during +2 Gz after blockade were 27.7 +/- 2.5 ml (diastolic) and 21.2 +/- 2.9 (systolic). The acceleration-induced changes in cardiovascular function, including the changes in ventricular volume, were not significantly different from those of the reflexive state. These results, therefore, do not reveal a substantial role for the autonomic nervous system in the regulation of left ventricular volume responses to the sudden cessation of G-induced peripheral blood pooling. Since the cessation of the G force induced essentially identical increases in left ventricular volumes and stroke volumes both before and after the autonomic blockade, it is concluded that the heart relied mainly upon the Frank-Starling mechanism to adapt to the changes in load.
Acceleration↗
Attenuation of vagal noradrenergic tachycardia by naloxone.
Electrical stimulation of the transected right vagus nerve in anesthetized and atropinized dogs produced tachycardia that was not attenuated by beta-adrenoceptor blockade. Naloxone in intravenous doses of 1 and 4 mg/kg antagonized the tachycardia evoked by nerve stimulation in a dose-dependent manner. However, the attenuation was maximal at approximately 55% of the control response. These results suggest that an endogenous opiate peptide(s) may have a mediator or modulator role in nonadrenergic tachycardia evoked by vagal nerve stimulation in anesthetized and atropinized dogs.
Adenylyl Cyclases↗
Cardiovascular regulation in canines during low-frequency acceleration.
Integrated, reflex, cardiovascular regulation in unanesthetized (tranquilized), chronically-instrumented dogs was studied using sinusoidal whole-body spinal-axis acceleration (+/- 2 Gz) at frequencies below 0.25 Hz. The participation of neurally mediated cardiac and vascular control mechanisms was examined by comparing the responses of the same animal in a normal (reflexive) state and ina pharmacologically blockaded (nonreflexive) state. Integrated neural mechanisms were found to be the most effective in minimizing acceleration-induced, arterial pressure disturbances for frequencies below 0.012 Hz; became progressively out of phase with the disturbances between 0.012 and 0.052 Hz, resulting in decreased effectiveness; and failed to significantly participate in the regulatory process for frequencies between 0.052 and 0.25 Hz, where "protection" was provided by the hydraulic and intrinsic biomechanical characteristics of the circulatory system. An analysis of the relative contribution of peripheral vascular and cardiac mechanisms indicated that 1) neurally mediated, systemic vascular responses were largest for frequency; 2) heart rate oscillations were large for frequencies below 0.052 Hz (corner frequency) and then decreased rapidly with increasing frequency; and 3) neurally mediated stroke volume oscillations were the largest for the lowest frequencies and decreased with increasing frequency.
Animals↗
Paraplegic use of the Orlau swivel walker: case report.
This case report describes the characteristics, biomechanics, fitting, training, advantages, and disadvantages of the Orlau swivel walker. Advantages of the walker include stability, easy mobility, and the ability of the wearer to ambulate with free hands. Disadvantages include slow velocity of locomotion, comparative metabolic inefficiency, awkwardness of getting into and from the standing position, and inability to be used on uneven surfaces. In a comparison of the metabolic costs and efficiency of the Orlau swivel walker, bilateral knee-ankle-foot orthoses, and a wheelchair, the swivel walker was least efficient (1.9ml O2/kg/m) in comparison to the knee-ankle-foot orthoses (0.9ml O2/kg/m) and the wheelchair (0.18ml O2/kg/m). However, in evaluating a means of locomotion, various factors besides metabolic costs need to be considered; these include efficiency, velocity, the physiologic and psychologic benefits of standing, and the patient's needs. When considering all these factors for an individual patient, the swivel walker may be an effective device for meeting the needs of many individuals with spinal cord injury.
Adult↗
Neural, hormonal and intrinsic mechanisms of cardiac control during acute coronary occlusion in the intact dog.
Three basic mechanisms may be involved in the control of cardiac function during acute coronary occlusion: (1) neural; (2) hormonal (circulating catecholamine); and (3) intrinsic (e.g. Frank--Starling law). The response of intact, sedated (Innovar-Vet, 0.08 cc/kg), chronically instrumented dogs to a 5 min left circumflex coronary occlusion was tested to delineate the relative roles of each of the above mechanisms. First, 6 innervated and 6 cardiac denervated dogs were examined. The major difference between groups was that the occlusion-induced tachycardia was significantly smaller in the denervated dogs than in the normally innervated animals (+10 +/- 7 vs +27 +/- 4/min, respectively, (mean +/- S.D.)). Changes in the first time derivative of left ventricular pressure (d(LVP)/dt) were similar (--898 +/- 556 vs --796 +/- 274 mm Hg/sec, denervated vs innervated). Decreases in stroke volume and mean arterial pressure were also similar in the two groups. The occlusion-induced tachycardia was compared in a second group of denervated dogs (n = 5) before and after administration of propranolol to examine the role of circulating catecholamines, and, by exclusion, to observe the response of the heart per se, independently of extrinsic control factors. The heart rate response was similar in both cases (+8 +/- 4 vs +6 +/- 4/min, unblocked vs blocked). Finally, blood pressure was prevented from falling during coronary occlusion in 3 normally innervated dogs by coupling the femoral artery to a reservoir of saline suspended above the animals. Blunting the input to the baroreceptors in this manner did not significantly change the size of the occlusion-induced tachycardia. We conclude that during acute coronary occlusion in dog: (1) the major role of the cardiac nerves involves modulating changes in the chronotropic state of the heart; (2) changes in d(LVP)/dt result principally from intrinsic phenomena linked to ischemia-induced alterations in myocardial performance; (3) changes in circulating catecholamines play only a minor role in controlling the heart during acute coronary occlusion in denervated dog; and (4) receptors located within the heart figure significantly in the etiology of the occlusion-induced tachycardia.
Acute Disease↗
Pressor response buffering by beta-adrenergic and cholinergic vasodilation in tranquilized dogs.
Buffering of alpha-receptor-mediated pressor responses by beta-adrenergic or cholinergic vasodilation in tranquilized, chronically instrumented gos was investigated. Increases in aortic pressure were produced in the same animal by intravenous injections of phenylephrine in the control state and in three successive experimental states by 1) pacing the heart to remove the reflex capability to lower heart rate, 2) pacing the heart and beta-blockade to remove beta-adrenergic vascular buffering, and 3) beta-blockade plus atropine to also remove cholinergic vascular buffering. The pressor response in each experimental state was greater than that in the state preceding it. With the combined beta-adrenergic and cholinergic blockade, the pressor response to an alpha-receptor stimulation was three times greater than that of the control state. From an analysis of the components of the pressor response, cardiac output, and peripheral resistance, it is suggested that normal buffering of an alpha-mediated pressor response may include beta-adrenergic and cholinergic vascular dilation in addition to a decrease in heart rate.
Adrenergic beta-Antagonists↗
Cardiac responses of dogs to nonsynchronous and heart synchronous whole-body vibration.
Changes in cardiac function produced by synchronizing vibration-induced forces with events in the cardiac cycle were compared to those for the nonsynchronous case in eight chronically instrumented, tranquilized dogs. The supine animals received sinusoidal, whole-body vibration (along the spinal +/- Gz axis) at a constant acceleration amplitude (+/- 0.75 G). The vibration frequency (2-3 Hz) was set equal to the paced heart frequency. Synchronization between vibration and cardiac cycles on a beat-by-beat basis produced a specific and sustained cardiovascular response; such a sustained response was not possible with nonsynchronous vibration. With synchronization, relationships could be found and sustained in which changes either exceeded or were below mean nonsynchronous levels, in some cases below previbration values. For the synchronous vs. nonsynchronous states, significant modification of cardiac function was reflected in parameters such as coronary flow (+15% to -34%) and myocardial oxygen consumption (+21% to -51%). Thus, whole-body oscillation acceleration (vibration) is a forcing function that can produce and maintain a particular cardiovascular response.
Animals↗
Modification of cardiac function by synchronized oscillating acceleration.
The sensitivity of selected cardiovascular (CV) responses to the physical stressor of External whole-body oscillating Acceleration Synchronized with the Electrocardiogram (EASE) was analyzed in 8 chronically instrumented tranquilized dogs. A sinusoidal acceleration wave form was imposed on the supine animals along the spinal (+/- Gz) axis at a constant amplitude of +/- 0.75 G, and a frequency equal to the paced-heart frequency (2--3 Hz). When the peak force was positive in early systole, and negative in early diastole, changes in myocardial oxygen consumption (MVo2, + 8%), mean coronary flow (MCF, + 8%), stroke volume (SV, + 15%), cardiac work (CW, + 19%) and the time derivative of left ventricular pressure (dP/dt, + 18%) were minimal in comparison to nonoscillatory control values. When the peak force was positive in early diastole and negative in late diastole and early systole, changes in MVo2 (+ 41%), MCF (+ 39%), SV (+ 33%), CW (+ 50%), and dP/dt (+ 31%) were maximal. Thus the capability of EASE to produce a range of desired sustained CV responses provides a basis for its potential diagnostic/therapeutic applications.
Acceleration↗
Parameters for assessing vibration-induced cardiovascular responses in awake dogs.
The vibration parameters for assessing the response of the cardiovascular system to whole-body vibration were studied. Six awake, chronically instrumented canines were restrained with their spines vertical, and exposed to GZ sinusoidal vibration of 2-12 HZ for a constant peak acceleration amplitude of +-1.0 G. Vibration exposures of 30 s with intervening recovery periods of 2 min were employed. The following variables were measured: mean heart rate (MHR), stroke volume (SV), mean aortic flow (MAF), mean aortic pressure (MAP), the peak net force transmitted to the canine/body weight (PNF/BW), and the vibration platform frequency (ft), displacement, and acceleration. The percentage change from control (no vibration) of MAF varied linearly with PNF/BW for all cases. MAF also varied linearly with the log MHR/ft for the number of dogs which primarily changed MHR during the vibration exposures. The response of MAP was minimal in all cases, indicating a decrease in total peripheral resistance with increasing PHF.
Animals↗
Microvascular pressure responses of second-generation rats chronically exposed to 2 G centrifugation.
The purpose of thses studies was to compare systemic arterial and microvascular pressures in the second generation of rats reared in a 2-G centrifuge with pressure data from animals subjected to 1 G centrifugation. Systemic arterial pressures were measured in anesthetized animals via carotid catheters and microvascular pressures were measured in mesenteric arterioles by a micropipette servo-null system. Systemic arterial pressures in the 1-G and 2-G groups were not significantly different from each other, but both were considerably higher than those reported for normal rats. In the microcirculation, pressures in the terminal arterioles (20 to 35 micron) were significantly higher in the 2-G animals, but pressures at the level of the smaller (10 to 15 micron) precapillary arterioles were not significantly different between the two groups. The pressure responses to intravenous infusion of norepinephrine were also compared in the two groups and found to be significantly less in the 2-G animals. It is concluded that both 1 G and 2 G chronic centrifugation will elevate arterial blood pressure, and that 2 G, of itself, will affect the pressure distribution in the microcirculation as well as attenuate the pressor effects of norepinephrine.
Animals↗
Experimental and analytical determinations of the mechanical impedance response of animals to vertical vibration.
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Animals↗
Changes in whole body force transmission of dogs exposed repeatedly to vibration.
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Adaptation, Physiological↗
Cardiovascular changes produced by brief whole-body vibration of animals.
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Animals↗
Spectral indices of cardiovascular adaptations to short-term simulated microgravity exposure.
We investigated the effects of exposure to microgravity on the baseline autonomic balance in cardiovascular regulation using spectral analysis of cardiovascular variables measured during supine rest. Heart rate, arterial pressure, radial flow, thoracic fluid impedance and central venous pressure were recorded from nine volunteers before and after simulated microgravity, produced by 20 hours of 6 degrees head down bedrest plus furosemide. Spectral powers increased after simulated microgravity in the low frequency region (centered at about 0.03 Hz) in arterial pressure, heart rate and radial flow, and decreased in the respiratory frequency region (centered at about 0.25 Hz) in heart rate. Reduced heart rate power in the respiratory frequency region indicates reduced parasympathetic influence on the heart. A concurrent increase in the low frequency power in arterial pressure, heart rate, and radial flow indicates increased sympathetic influence. These results suggest that the baseline autonomic balance in cardiovascular regulation is shifted towards increased sympathetic and decreased parasympathetic influence after exposure to short-term simulated microgravity.
Adaptation, Physiological↗