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T Natsuyama

Publications and source records attributed to T Natsuyama.

10 recordsLinked to original sources
PubMed1992

Mechanism underlying the changes in plasma potassium concentration during infusion of isosmotic nonelectrolyte solution.

Generally, during infusion of an isosmotic nonelectrolyte solution that permeates the cell membrane, plasma K+ concentration ([K+]pl) either does not change or it increases slightly. The mechanism underlying this [K+]pl change has not been clarified. We continuously monitored the [K+]pl and plasma Na+ concentration ([Na+]pl) for 10 min during isosmotic mannitol infusion of 1.6 ml/100 g body weight in rats with intact kidney function (intact mannitol group). In addition, in nephrectomized rats, we compared the [K+]pl change during infusion with isosmotic mannitol (which permeates the cell membrane; mannitol nephrectomized group) with that during infusion with isosmotic sucrose (which does not permeate the cell membrane; sucrose nephrectomized group) to evaluate the effect of cell volume regulation. In the intact mannitol group, [Na+]pl decreased with dilution, and [K+]pl remained relatively constant. In the sucrose nephrectomized group, [K+]pl decreased by the same percentage as [Na+]pl and gradually increased to greater than the control level. In the mannitol nephrectomized group, however, [K+]pl increased immediately after the beginning of the infusion and reached the same level as that in the sucrose nephrectomized group. To confirm that the difference in [K+]pl between the mannitol and sucrose nephrectomized groups was dependent on cell volume regulation, we investigated the changes in mean corpuscular volume of red blood cells, using a Coulter counter. This value remained constant during isosmotic sucrose infusion but increased during isosmotic mannitol infusion, returning to the original volume after the infusion. We kept [HCO3-] and pH constant throughout the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Vascular viscoelasticity of perfused rat hindquarters.

To determine viscoelastic features of the rat hindquarters vasculature, we measured pressure-volume curves. Male Wistar rats were transected at the lumbar level, and the perfused hindquarters were oxygenated with a hollow fiber artificial lung. The blood volume was measured by counting 51Cr-labeled red cells led to a gamma counter through an extracorporeal circuit at a constant rate. With continuous monitoring of the venous pressure and circulating blood volume, saline was infused into the circuit from a venous branch for 5 min [1.2 +/- 0.3% (SD) of tissue weight] followed by a 10-min recovery phase. In the recovery phase, the venous pressure promptly declined to the preinfusion level, whereas the circulating blood volume decreased more slowly. This implied vascular stress relaxation of the hindquarters. Maxwell's viscoelastic model, consisting of a spring component and a viscous component, was applied to analyze the venous pressure-volume diagram. With a curve-fitting method, the calculated vascular compliance and relaxation time (a time constant of stress relaxation) were 1.31 +/- 0.14 ml.mmHg-1.kg-1 and 15.7 +/- 4.0 min (means +/- SE), respectively. The value of compliance of the hindquarters was smaller than those of visceral organs reported. In addition, the value for relaxation time suggests that the viscous response of the vasculature simultaneously overlaps change in blood volume due to extravascular fluid shift during the postinfusion period.

Animals↗
PubMed1991

Regulation of vascular compliance and stress relaxation by the sympathetic nervous system.

We measured the changes in central venous pressure (CVP) and circulating blood volume (CBV) in dogs consequent to fluid infusion under halothane anesthesia, and compared the CVP and CBV responses to those obtained after blocking the autonomic nervous system by total spinal anesthesia (TSA) and stimulating the alpha receptor with methoxamine (MTX). Under TSA, the change in CVP consequent to fluid infusion was less than that under halothane anesthesia, while with MTX, the change in CVP was larger than that under halothane anesthesia. The recovery time of CVP response toward the baseline level after the end of fluid infusion was fastest under halothane anesthesia, while the recovery time of CVP was two times longer under TSA and MTX. Based on the relationship between changes in CVP and BV, we quantified effective vascular compliance and stress relaxation using mathematical analysis. The effective vascular compliance increased to 13.3 +/- 3.2 ml.mmHg-1.kg-1 under TSA as compared to 5.6 +/- 0.3 ml.mmHg-1.kg-1 under halothane anesthesia, and it decreased to 2.6 +/- 0.2 ml.mmHg-1.kg-1 with MTX. Stress relaxation was determined as the time constant in the unit response of CVP. The time constant for stress relaxation was 39 +/- 7 min under halothane, 74 +/- 12 min with TSA, and 92 +/- 25 min with MTX. These results suggest that the autonomic nervous system modifies cardiac preload by changing effective vascular compliance and stress relaxation.

Anesthesia, Spinal↗
PubMed1990

Effect of nicardipine hydrochloride on circulating blood volume and vascular compliance in dogs.

We studied the effect of nicardipine on the canine cardiovascular system, especially on total blood volume and vascular compliance. Under light halothane anesthesia, nicardipine decreased total blood volume significantly (from 80.0 +/- 8.4 ml/kg in the control state to 75.3 +/- 8.0 ml/kg under nicardipine administration, p less than 0.01), while it increased central circulating blood volume (from 17.1 +/- 5.9 ml/kg to 25.5 +/- 8.2 ml/kg, p less than 0.01), increased cardiac output and central venous pressure, and decreased mean arterial pressure (from 134.3 +/- 16.2 mmHg to 93.9 +/- 17.1 mmHg, p less than 0.01) and total peripheral resistance. Vascular compliance derived from fluid infusion experiments showed a significant decrease (from 8.9 +/- 3.8 ml/mmHg/kg to 5.5 +/- 8.0 ml/mmHg/kg, p less than 0.01). In addition to the vasodilatory action of nicardipine on arteries, these findings also suggest that 1) nicardipine causes a fluid shift from the vascular to the interstitial fluid space as a result of increased capillary pressure, 2) it increases preload through blood redistribution from the peripheral to the central circulation, and 3) it decreases compliance of the vessels, perhaps due to an indirect splanchnic venoconstriction.

Animals↗
PubMed1989

[A newly devised continuous catheter flush system for arterial pressure monitoring].

Since Gardner et al. demonstrated a useful continuous catheter flush system in 1970, various systems for blood pressure monitoring have been commercialized. However, some problems have not been solved yet, such as hazard of embolism, infarction, unexpected infusion of large amount of fluid etc.. We have introduced a new type of flush system. which consists of disposable plastic unit with a one-way valve newly developed by us (SAT-route) and a syringe pump (Terumo STC-521). Using this system, only 0.5 ml.hr-1 infusion of heparinized saline was sufficient to prevent the formation of thrombus. Flushing was easily achieved by only pushing the purge button of the pump. As a result, simple, safe and high fidelity pressure monitoring was achieved without much altering the waveform of arterial pressure during flushing. The dynamic frequency response obtained from a square wave test was excellent, with natural frequency of about 40 Hz and damping coefficient of about 0.3. This system is useful especially for perioperative management of small children undergoing cardiac surgery, who require an exquisite infusion therapy and fluid restriction.

Blood Pressure Monitors↗
PubMed1988

Effect of adenosine triphosphate on canine renal circulation.

The effect of adenosine triphosphate (ATP) on systemic and renal hemodynamics was studied in seven dogs anesthetized with pentobarbital and enflurane. Adenosine triphosphate was given via the vena cava, the left atrium, and the abdominal aorta close to the left renal artery. Bolus injection of ATP in the vena cava showed a dose-dependent decrease of mean arterial pressure and renal blood flow, while cardiac output showed only a slight change. Continuous infusion of ATP in the vena cava or the left atrium showed stable hypotension, decrease of renal blood flow, with slight change of cardiac output. Despite the decrease of total peripheral resistance (TRP), renal vascular resistance (RVR) increased significantly in all cases. However, the continuous infusion of ATP into the abdominal aorta close to the left renal artery caused variable responses of systemic arterial pressure and a significant decrease of the RVR. These results suggest that ATP has a renal vasodilator effect only when given directly into the renal artery, and that a renal vasoconstriction occurs responding to the systemic effect of ATP when ATP is given intravenously or into the left atrium.

Adenosine Triphosphate↗