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Biomedical subjects

R J Rivers

Publications and source records attributed to R J Rivers.

30 records · Page 2Linked to original sources
PubMed1978

Atrial pacing from the coronary vein. Ten-year experience in 50 patients with implanted pervenous pacemakers.

During the past ten years, pervenous atrial pacemakers have been implanted in 50 patients (mean age 68 years, 60% males) using an electrode positioned in the coronary vein. The indications for atrial pacing were symptomatic sinus bradycardia (72%), atrial brady-tachy syndrome (20%), and recurrent tachyarrhythmias (8%). Atrial pacemakers have been implanted for a total of 1531 pacing months, average 31 months per patient, median 26 months and range 3-97 months. Effective atrial pacing has been achieved with Medtronic model 5818 and 6904 electrodes. Unipolar or bipolar atrial pacing has been equally effective, and commercially available Medtronic 5950, Cordis 162 and CPI 602 pulse generators have been utilized without difficulty. A total of 11 electrode related malpacing events occurred in the ten-year period with a malpacing event rate of 10% in the first pacing month, 1.1% per paced month during the next six months, and 0.25% per paced month thereafter. Life table analysis reveals that effective atrial pacing was achieved in 76% of the patients during a follow-up of more than five years. This experience substantiates the long-term safety and effectiveness of atrial pacing from the coronary vein using standard pacemaker electrodes and generators.

Aged↗
PubMedDate not supplied

Network vascular communication initiated by increases in tissue adenosine.

Vascular communication of vasomotor signals appears to coordinate the distribution of tissue blood flow. This study was performed to determine whether elevated tissue concentrations of adenosine or nitric oxide could induce vascular communicating signals. To test this, remote arteriolar responses were tested when drugs were applied either directly to an arteriole ( approximately 20 microm diameter), or into the tissue in a region (with no vessels over 10 microm in diameter) that was 500 microm away from the arteriole and that bore no defined relationship to the flow path of the remote arteriole. In anesthetized hamster cheek pouch (n = 25), or cremaster muscle (n = 10), remote arteriolar responses were measured in response to nitric oxide (NO) donors (10(-5) to 10(-3) M), adenosine (10(-5) to 10(-3) M), or papaverine (10(-5) to 10(-2) M) applied for 40-120 s. Papaverine caused no remote response when applied directly while adenosine and NO donors caused similar, late-onset (10-20 s), dose-dependent, remote responses in both preparations. Remarkably however, only adenosine initiated a consistent remote arteriolar dilation when applied to the tissue site. Thus, increases in tissue adenosine may be critical for vascular communication of metabolic demands without regard to the specific blood flow path.

Adenosine↗
PubMedDate not supplied

Nonvasomotor influence of sodium nitroprusside on arteriolar remote response to methacholine.

Vascular communication functions to facilitate blood distribution within tissues and can be demonstrated as conducted vasomotor responses. This study was designed to determine if local application of sodium nitroprusside (SNP) would affect arteriolar function at remote sites. In the cheek pouch of anesthetized hamsters, local application of SNP and nifedipine caused arteriolar dilation only at the site of application (7.1 +/- 0.5 and 7.4 +/- 0.6 microm), but not at remote sites. The application of SNP enhanced subsequent remote, nitric oxide (NO)-independent dilation in response to methacholine, which was applied at a site upstream from the SNP application site (6.7 +/- 0.7 versus 4.5 +/- 0.7 microm for methacholine alone). This potentiating effect was also observed following application of 3-morpholinosydnonimine, but not following nifedipine. This nonvasomotor influence of SNP was not affected by N(omega)-nitro-L-arginine (L-NA), tetrodotoxin (TTX), Gap 27 peptide or halothane. Attenuated local dilation in response to methacholine by L-NA could be partially recovered following downstream application of SNP, suggesting that SNP-induced potentiation was associated with enhanced vasodilatory signals at the methacholine application site. Thus, our results suggest that SNP induces nonvasomotor signals in arterioles to affect the network distribution of blood flow. Intrinsic NO, TTX-sensitive Na(+) channels and gap junctional communication do not seem to play a major role in the conduction of the nonvasomotor signals.

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