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Biomedical subjects

C E Constantinou

Publications and source records attributed to C E Constantinou.

At least 73 records · Page 4Linked to original sources
PubMed1981

Multiple-coupled pacemaker system in renal pelvis of the unicalyceal kidney.

The characteristics of spontaneous contractility in the renal pelvis were examined in the unicalyceal kidney of the rabbit. In vitro isometric studies were done on whole as well as renal pelvic segments dissected longitudinally and radially. The results show that the contractile frequency of isolated segments was highest in the proximal region (4.188 +/- 0.162 min-1) and decreased distally to (2.178 +/- 0.330 min-1). There was no significant frequency gradient in the circumferential direction. A modulation of wave form (waxing and waning phenomena) was observed in both the proximal and middle regions of the pelvis. Based on these results, a simulation of the renal pelvic activity was made by using a chain of coupled linear oscillators. At high values of coupling a pacemaker contraction of the renal pelvis was reproduced by the coupled oscillator model. The modulation of wave form was observed when the coupling of the circumferential direction was weak. These results are discussed in the context of the hierarchically organized multiple-coupled pacemaker system, which characterizes an integrative activity of the unicalyceal renal pelvis.

Animals↗
PubMed1981

Total [Na+] and [K+] gradient in the pyeloureter.

The gradient of cellular [Na+] on [K+] ion within the renal pelvis of the rabbit was correlated with the autorhythmicity of the proximal, middle, distal and ureteropelvic regions of this structure. The results show that the maximum frequency of spontaneous pacemaker contractions occur at the proximal pelvis with a mean frequency of 4.97 +/- 0.85 contractions/min, a mean [Na+] of 91.0 +/- 33.3 mEq/kg net weight, a mean [K+] of 18.9 +/- 6.0 mEq/kg net weight. The frequency of spontaneous activity from the middle pelvis and distal pelvis decreases to mean values of 2.76 +/- 0.60 and 1.82 +/- 0.56 contractions/min. The corresponding values for [Na+] and [K+] are 78.0 +/- 27.7 and 11.8 +/- 4.7 for the middle pelvis and 66.6 +/- 32.7 and 9.75 +/- 3.4 for the distal pelvis, respectively. Normalized regression curves indicate a [Na+]gradient variation of delta [Na+] = 67.1 +/- 0.07 delta F and a [K+] gradient of delta [K+] = 39.8 - 0.06 delta F + 0.01 delta F2. Spatially, the variation of [Na+] and [K+] with distance. D, within the pelvis is given by [Na+] = 119 - 14D + D2 and [K+] = 26 - 11D + 2D2. It is concluded from this study that there is a frequency gradient between proximal renal pelvis and ureteropelvic junction which is significantly interdependent upon the cellular [Na+] on [K+] concentration gradient.

Animals↗
PubMed1981

Gradient of total [Ca++] in the renal pelvis.

The [Ca++] gradient within the rabbit renal pelvis was compared to its inherent pacemaker frequency. The pelvis was removed from the rabbit, sectioned, and [Ca++] ions assayed using wet ash techniques and atomic absorption spectrophotometry. Contraction frequency was measured isometrically in vitro. In the bisected pelvis it was found that both [Cu++] levels and contraction frequency were highest in the proximal section, 9.02 +/- 4.62 mEq/kg, and lower in the distal section, 6.59 +/- 2.43 mEq/kg wet weight. The mean frequency of contraction decreased from 3.69 +/- 0.81 to 2.41 +/- 0.49 min-1 in the proximal and distal regions, respectively.

Animals↗
PubMed1980

Urodynamic analysis of urethral, vesical and perivesical pressure distribution in the healthy female.

The transmission of intra-abdominal pressures to the urethra of the healthy female is examined with respect to cough, Valsalva and holding stimuli. A new method of recording urethral pressures using a four-channel, perfused gap catheter specifically constructed for this investigation is used. The results show that the increase of urethral pressure to stimuli is magnified at the distal urethra to a significant degree. This magnification is significantly higher than that expected by direct intra-abdominal transmission. Anatomically, the focus of urethral magnification of pressures is located 2-3 mm distal to the external urethral sphincter. The data provided from this study indicate that the mechanism of action of urethral closure to stress is active and does not directly correspond to the transmission properties of the lower urinary tract to stresses. Evidence supporting this mechanism is drawn also from the differential behavior of the proximal and distal regions of the urethra to the initiation and cessation of voiding.

Adolescent↗
PubMed1980

Hydronephrotic alterations in calyceal and renal pelvic pacemaker function of the in vitro pyeloureteral system.

There are regional variations of the amplitude, frequency and waveform of spontaneous contractions within the isolated renal pelvis and calyx of the multicalyceal pyeloureter of the pig. The contractility of these structures was studied in normal and hydronephrotic preparations. Tissues were obtained from normal and chronically obstructed animals. In 20 normal preparations, the contractile frequency of the renal pelvis was 4.9 +/- 2.1 contractions/min, while that of the calyx was 9.5 +/- 2.2 (mean +/- SD). The recorded amplitude was 0.95 +/- 0.92 and 0.45 +/- 0.61 g, respectively. The waveform of the calyceal contractility approximated the sinusoid demonstrating a slow rise and fall in tension, while the waveform of renal pelvic smooth muscle demonstrated a faster increase in tension. Obstruction and hydronephrosis produced a minimal alteration in the frequency and amplitude of the calyceal structures, 9.1 +/- 2.2 contractions/min and 0.71 +/- 0.49 g, respectively. Hydronephrotic renal pelves demonstrated a significant increase in the frequency of spontaneous contractility 8.0 +/- 4.2 contractions/min with no change in the mean amplitude of contraction 0.88 +/- 0.90 g. These data suggest that obstruction alters the frequency of isolated renal pelvic contraction so that they approximate the frequency of isolated calyceal contractions.

Animals↗
PubMed1979

Velocity gradient and contraction frequency of the pyeloureteral system.

An optical detection method, using video imaging, is used to quantitatively record the frequency and velocity profile of the renal pelvis of the rabbit. It is demonstrated that concentric waves originating at the periphery of the pelvis have an initial velocity of 3.2 cm/sec, accelerating toward the pelviureteral junction reaching a final velocity of 6.4 cm/sec.

Animals↗
PubMed1979

Assessment of pyeloureteral function using a flow velocity and cross-sectional diameter probe.

The response of the healthy pyeloureteral system of the pig to stepwise increments of urine flow was measured using a flow-velocity, diameter probe. The following urodynamic parameters were measured: renal pelvic pressure, ureteral flow-velocity and diameter, and associated bolus volume in the range of urine flow rates of 0.3 to 10 ml per min. The results show that the diameter sensoring portion of this probe can reliably sense ureteral peristalsis over the entire range of urine flow rates; small alterations in ureteral diameter occurring in dilated ureters after high diuretic loads can also be detected. Data obtained using the flow-velocity portion of this probe indicate that at urine flow rates less than 0.5 ml per min flow-velocity changes of a bolus can be reliably identified. At these flow rates the maximum flow-velocity occurs at the leading edge of the bolus and is invariant with the size of the bolus. At urine flow rates more than 1 ml per min the flow-velocity curve is polyphasic, indicative of an alteration in the mechanism of urine transport by the ureter at these flows. Collectively, data obtained using this probe provide dynamic information concerning the physiologic properties of the upper urinary tract not currently attainable in existing pressure/flow methodologies.

Animals↗
PubMed1978

Frequency gradient in the autorhythmicity of the pyeloureteral pacemaker system.

The pacemaker properties of the various regions of isolated segments of the rabbit renal pelvis were examined. The results show that pacemaker frequency and waveform of contraction change significantly within the renal pelvis. The highest frequency was encountered at the fornix, while the ureteropelvic junction is lowest.

Animals↗
PubMed1978

Contractility of the pyeloureteral pacemaker system.

The patterns of mechanical contractility in the pyeloureteral pacemaker system were explored in an effort to identify some of the properties of initiating ureteral peristalsis. Rabbit renal pelvises were studied in vivo, in vitro perfused with Krebs solution through the renal artery and in segments. The results show that all segments of renal pelvic smooth muscle are capable of spontaneous contractions, the fornix having the highest frequency with respect to the pelvis. It is also demonstrated that the pelvic contractile wave concentrically accelerates along the renal pelvic perimeter. Under steady state conditions, renal pelvic pressure undergoes a low frequency oscillation having a period of 1--2 min which is flow-rate dependent. The results are discussed within the context of the pyeloureteral pacemaker system and the possible existence of a feedback mechanisms between the renal pelvis and the perfusion of the kidney.

Animals↗
PubMed1977

Pacemaker system in the control of ureteral peristaltic rate in the multicalyceal kidney of the pig.

Temporal and distributive properties of ureteral peristaltic contractions in the anesthetized pig have been examined. Interperistaltic time intervals have been recorded, and their frequency during different urine flow rates has been compared. The results show that ureteral peristalsis is increased at high urine flow rates to a maximum of approximately 0.06 Hz. It is further shown from the interperistaltic histograms that ureteral contractions are not clustered into a discreet multimodal spectrum. This represents the first evidence that the multicalyceal kidney has a system of pacemakers of differing fundamental frequencies, tending toward synchronism as urine flow increases.

Animals↗
PubMed1976

The incidence of ecotpic peristaltic contractions.

The continuity of ureteral peristaltic conduction along the ureter of the dog is examined using two pairs of extracellular macroelectrodes. At urine flow rates below 3 ml/min, ureteral contractions initiated by the pacemaker are propagated without interruption along the entire length of the ureter, and at sustained diuretic levels greater than 3-5 ml/min, ectopic peristaltic and retrograde events may be initiated along the length of the ureter. Also, continued maintenance of diuresis results in decremental conduction along the upper third of the ureter with the ultimate possiblity of pacemaker failure.

Animals↗
PubMed1976

Renal pelivic pacemaker arrhythmias induced by pentothal anesthesia.

The influence of Pentothal anesthesia in blocking the mechanism intimating ureteral peristalsis in the dog is examined. Pressure measurements of pacemaker rhythmicity were made through renal cortical catheterization of the renal pelvis. Simultaneously, ureteral recordings were made by extracellular electromyography of the ureteral smooth muscle wall. It is shown that Pentothal anesthesia transiently blocks the spontaneous and rhythmic contractions of the renal pelvis and inhibits the generation of ureteral peristaltic contractions. It is demonstrated that repeated or prolonged pacemaker blockade results in an open ureteropelvic junction and aperistalsis. A discussion of the possible implication of these observations is given.

Anesthesia↗
PubMed1976

Urodynamics of the upper urinary tract.

The control of ureteral peristaltic contractions by a pacemaker system is shown in a series of experimental observations on the anesthetized dog. Data are presented to illustrate the influence of pacemaker frequency on ureteral rate and bolus volume during oliguria and transient diuresis. Pacemaker frequency was determined from the pressure wave form of the renal pelvis and peristaltic rate was measured electrophysiologically. The bolus volume associated with each peristaltic contraction was recorded by a drop counter and correlated with pacemaker and ureteral activity. The results show that the pacemaker frequency remains constant over urine flow rates in the range of 0.3 to 15 ml per min. It is also shown that the pacemaker frequency is constant during transient increases in flow rate of more than one order of magnitude. During diuresis, the peristaltic rate changes in quantum steps determined by the fundamental frequency of the pacemaker, and at flow rates greater than 2 ml per min the ureter contracts at the pacemaker rate. Further increases in flow are accommodated by increasing the amount of urine transported by each bolus. The urologic importance of these observations on pacemaker function is discussed in terms of the unicalyceal and multicalyceal upper urinary tract.

Animals↗
PubMed1975

Ureteral pacemaker potentials recorded with the sucrose gap technique.

Ureteral contractions occur at intervals which are integral multiples of the period of pacemaker potentials recorded in vitro from the renal pelvis with a sucrose gap, suggesting that a gating mechanism in the pyeloureter regulates the rate at which the pacemaker initiates contractions.

Action Potentials↗