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Biomedical subjects

E Koushanpour

Publications and source records attributed to E Koushanpour.

At least 19 recordsLinked to original sources
PubMed1987

Blockade of contralateral carotid sinus nerve enhances ipsilateral nerve action potentials under halothane anaesthesia.

In 10 dogs, one carotid sinus was isolated from the systemic circulation without disturbing its sympathetic innervation. The isolated sinus was connected to a servo-controlled pressure generator which kept mean intrasinus pressure, pulse pressure, and frequency of pulsation constant. The carotid sinus baroreceptor nerve action potentials (NAP) were measured, together with the intransinus and systemic pressures. Following control measurements, the end-tidal concentrations of halothane in oxygen were varied between 0.0 and 2%, in random increments of 0.5%, each with 30 min of stabilization. The carotid sinus NAP response to halothane was biphasic in a dose-dependent manner. The series was repeated after neural blockade of the contralateral sinus with 1% lignocaine 2-3 ml. This blockade enhanced all NAP responses (P less than 0.001), suggesting that a central inhibitory effect, initiated by the contralateral sinus, had been removed.

Action Potentials↗
PubMed1987

Partition of carotid baroreceptor response in two-kidney renal hypertensive dogs.

This study evaluated the mechanism of carotid sinus baroreceptor resetting in two-kidney one-clip Goldblatt hypertension in dogs by partitioning the resetting between carotid sinus wall compliance and receptor neural elements. With dogs under halothane anesthesia, the left renal artery was constricted 70-80% with a Goldblatt clamp without disturbing the contralateral kidney. Ten weeks later, when mean blood pressure had risen to 151 +/- 6 mmHg (means +/- SE) compared with 105 +/- 5 mmHg in controls, we measured simultaneously whole nerve action potentials (N) and carotid sinus volume (V) during step changes in intrasinus pressure (P). Hypertensive N vs. P relationship was sigmoid shaped and shifted toward the P-axis compared with controls. Hypertensive V vs. P relationship was not significantly different from controls. The hypertensive N vs. V relationship derived from the composite plots of N vs. P and V vs. P was sigmoid shaped and shifted toward the V-axis compared with controls. These results suggest that the resetting of baroreceptors is due to changes in receptor properties rather than carotid sinus wall compliance.

Action Potentials↗
PubMed1984

Renal tissue oxygenation following induced hypotension in dogs.

Renal oxygenation was studied during induced hypotension in mongrel dogs, anaesthetized with 1-1.5% halothane in oxygen. Hypotension was induced with an infusion i.v. of sodium nitroprusside (SNP) 70 +/- 17 micrograms kg-1 min-1 (mean +/- SEM) or trimetaphan (TMP) 36 +/- 16 micrograms kg-1 min-1, or by controlled arterial haemorrhage (45 +/- 6 ml/kg of body weight). Mean arterial pressure (MAP), cortical (Pcto2) and medullary (Pmto2) tissue oxygen tensions, arterial (Pao2), renal venous (Prvo2), and urine (Puo2) oxygen tensions were measured during the 40-min control, hypotension, and recovery periods. MAP was decreased to approximately 60% of the control value. Pcto2 decreased significantly (P less than 0.05) in all three groups while Pmto2 decreased significantly only in the haemorrhage group. Upon restoration of MAP to normal values, renal tissue oxygen tensions recovered in all groups, somewhat more rapidly in the SNP group. There were no significant differences in Pao2, Prvo2, and Puo2 during control, hypotension and recovery periods in the three groups. Tissue oxygen tension values followed the changes in MAP, but were not hypoxic, leading us to believe that both SNP and TMP are hypotensive agents safe for the kidney.

Animals↗
PubMed1984

Local versus central effect of halothane on carotid sinus baroreceptor function.

Depressive effect of halothane on carotid sinus baroreceptor function may be due to direct local action, in the CNS, or both. Paris of dogs were anesthetized with pentobarbital and ventilated with oxygen. The carotid sinus of the recipient dog was isolated and perfused with blood from the common carotid artery of the donor dog. Blood from the recipient sinus was returned through its external carotid to the donor common carotid. Thus, both carotid sinuses of the donor and the contralateral carotid sinus of the recipient dog received uninterrupted circulation. Carotid sinus nerve action potentials and lingual artery pressure of the isolated recipient sinus were recorded before and during steady state end-tidal halothane concentrations of 0, 0.5, 1.0, 1.5, 2.0, and 2.5% in oxygen, given randomly first to the donor dog (to evaluate direct local effect) and then to the recipient dog (to determine central effect). The dog not given halothane received pentobarbital. Plots of normalized nerve activity versus halothane concentrations showed approximately zero slope when the donor was given halothane but showed significant decrease in nerve activity when the recipient was given halothane. Halothane appears to have no direct local effect but causes depression of baroreceptor nerve activity, possibly via CNS inhibition of sympathetic efferents to the carotid sinus.

Action Potentials↗
PubMed1982

Trimethaphan-induced hypotension: effect on renal function.

This study was designed to evaluate the effects of trimethaphan-induced hypotension on renal function in healthy young patients undergoing maxillofacial surgery. Anaesthesia was induced with thiopentone and was maintained with halothane 1.5-2.0 per cent in oxygen. Each patient served as his own control, and data were analyzed using the paired t-test. Trimethaphan was infused at a rate of 45-52 microgram.kg-1.min-1 for an average hypotensive period of 53 +/- 4 (mean +/- SEM) minutes to reduce the mean arterial pressure (MAP) to 49 +/- 2 torr. Endogenous creatinine clearance, urinary Po2, sodium reabsorption rate (Tna), and serum and urine osmolalities were determined before, during and after arterial hypotension with trimethaphan. Urine flow averaged 2.9 +/- 1 ml/min during the period of hypotension. Endogenous creatinine clearance and Tna were significantly decreased (p less than 0.05) in the hypotensive period. These values returned to normal levels within one hour upon discontinuation of trimethaphan and restoration of blood pressure. We found no statistical difference in urine Po2, and serum and urine osmolalities during control, hypotensive and recovery periods. These results suggest that medullary renal tissue oxygenation, an index of tissue viability, may have remained adequate despite a significant reduction in endogenous creatinine clearance during the hypotensive period. Furthermore, it appears that the effect of trimethaphan-induced hypotension on renal function is similar to the sodium nitroprusside-induced hypotension in man which we have reported previously.

Anesthesia↗
PubMed1982

A planimetric technique for measuring deformation of the carotid sinus region.

This paper describes a planimetric technique for measuring the volume of the carotid sinus region from still photographs taken during pressure and volume forcings. The method consists of first digitizing the curves defining the boundary of the carotid sinus and then calculating its volume by assuming that the carotid sinus region is made up of a finite number of circular "pancake" slices. Plots of the calculated volume (Vc) vs. applied pressure forcings (P) were compared with plots of injected volume (Vi) vs. recorded pressure to assess the sensitivity of the method used to calculate volume changes from still photographs. The plots of Vc vs. P were remarkably similar to the plots of Vi vs. recorded pressure, and a plot of Vc vs. Vi was linear, suggesting that this method provides a good estimate of volume changes. Application of this method can yield useful data on mechanisms of the baroreceptor process.

Animals↗
PubMed1981

Partition of carotid sinus baroreceptor response in dogs with chronic renal hypertension.

This study was designed to determine whether resetting of the carotid sinus baroreceptors in chronic renal hypertension is due to altered distensibility of the wall, or changes in the properties of the receptor elements, or both. Dogs were made hypertensive by 50% constriction of the left renal artery with a Goldblatt clamp and by right nephrectomy one week later. Five to nine weeks after nephrectomy, when mean blood pressure had risen by 35-46 mm Hg, the isolated carotid sinus wall deformation, measured from still photographs, and gross baroreceptor nerve action potentials (N) were recorded in response to step intrasinus pressure forcings (P), ranging from zero to 300 mm Hg, in increments of 25 mm Hg. Measured wall deformation was converted to strain-energy density (SED), a scalar value, as the best indicator of the mechanical state of the sinus wall. Plots of N vs. P data followed an S-shaped pattern, but were shifted toward the P-axis, as compared to controls. Plots of SED vs. P, though linear over most of the pressure range, were shifted toward the SED-axis, as compared to controls. A plot of N vs. SED, derived from the composite plots of N vs. P and SED vs. P, followed an S-shaped pattern and also was shifted toward the SED-axis. We conclude that the nonlinearity in the N vs. P curve is due largely to the inability of the receptor elements to respond to increasing wall strain and to resetting of the baroreceptors due to changes in the receptor properties rather than in the wall elements.

Action Potentials↗