Severe retinal degeneration in a patient with Canavan disease

Background: Canavan disease is an autosomal recessive, neurodegenerative disorder caused by mutations in ASPA, a gene encoding the enzyme aspartoacylase. Patients present with macrocephaly, developmental delay, hypotonia, vision impairment and accumulation of N-acetylaspartic acid. Progressive white matter changes occur in the central nervous system. The disorder is often fatal in early childhood, but milder forms exist. Materials and methods: Case report. Results: We present the case of a 31-year-old male with mild/juvenile Canavan disease who had severe vision loss due to a retinal degeneration resembling retinitis pigmentosa. Prior to this case, vision loss in Canavan disease had been attributed to optic atrophy based on fundoscopic evidence of optic nerve pallor. Investigations for an alternative cause for our patient's retinal degeneration were non-revealing. Conclusion: We wonder if retinal degeneration may not have been previously recognized as a feature of Canavan disease. We highlight findings from animal models of Canavan disease to further support the association between Canavan disease and retinal degeneration.

Analysis of a large choroideremia dataset does not suggest a preference for inclusion of certain genotypes in future trials of gene therapy

Background

Choroideremia (CHM) is an X‐linked degeneration of the retinal pigment epithelium, photoreceptors, and choroid, which causes nyctalopia and progressive constriction of visual fields leading to blindness. The CHM gene encodes Rab escort protein 1 (REP‐1). In this work, we reviewed the phenotypes and genotypes of affected males with the purpose of understanding the functional effects of CHM mutations and their relationship with the phenotypes.

Methods

A retrospective review of 128 affected males was performed analyzing the onset of symptoms, visual acuity, and visual fields with respect to their mutations in the CHM gene.

Results

In rank order, reflecting data from this report, the most common mutations found in the CHM gene were nonsense mutations (41%), exon deletions (37%), and splice sites (14%) associated with a loss of functional protein. In the pool of 106 CHM mutations, we discovered four novel missense mutations (c.238C>T; p.L80F, c.819G>T; p.Q273H, c.1327A>G; p.M443V, and c.1370C>T; p.L457P) predicted to be severe changes affecting protein stability and folding with the effect similar to that of other types of mutations. No significant genotype–phenotype correlation was found with respect to the onset of nyctalopia, the onset of other visual symptoms, visual acuity, or width of visual fields.

Conclusion

There is no evidence to support exclusion of CHM patients from clinical trials based on their genotypes or any potential genotype–phenotype correlations.

Choroideremia research: Report and perspectives on the second international scientific symposium for choroideremia

PURPOSE

To discuss progress in research on choroideremia (CHM) and related retinopathies with special emphasis on gene therapy approaches.

METHODS

Biomedical and clinical researchers from across the world as well as representatives of the social science research community were convened to the 2nd International Scientific Symposium for Choroideremia in Denver, Colorado in June 2014 to enhance our understanding of CHM and accelerate the translation of research to clinical application for the benefit of those affected by CHM.

RESULTS

Pre-clinical research using cell and animal models continues to further our understanding in the pathogenesis of CHM as well as to demonstrate proof-of-concept for gene transfer strategies. With the advent of modern imaging technology, better outcome measures are being defined for upcoming clinical trials. Results from the first gene therapy trial in CHM show promise, with sustained visual improvement over 6 months post-treatment. Current and next-generation gene transfer approaches may make targeted vector delivery possible in the future for CHM and other inherited retinal diseases.

CONCLUSIONS

While no accepted therapies exist for CHM, promising approaches using viral-vectored gene therapy and cell therapies are entering clinical trials for eye diseases, with gene therapy trials underway for CHM.

Changes in rod and cone-driven oscillatory potentials in the aging human retina

PURPOSE

We recorded oscillatory potentials (OPs) to document how age impacts on rod- and cone-driven inner retina function.

METHODS

Dark- and light-adapted electroretinogram (ERG) luminance-response functions were recorded in healthy human subjects aged 20 to 39, 40 to 59, and 60 to 82 years. Raw ERG traces (0.1-300 Hz) were filtered (75-300 Hz) to measure OPs trough-to-peak in the time-amplitude domain. Morlet wavelet transform (MWT) allowed documenting OPs time-amplitude-frequency distribution from raw traces.

RESULTS

Under dark adaptation, both methods revealed reduced OP amplitudes and prolonged implicit times by 40 years of age. The MWT identified a high-frequency band as the main oscillator, which frequency (150-155 Hz) was unaffected by age. Under light adaptation, most OP peaks were delayed by 40 years of age. Peak-trough measures yielded inconsistent results in relation to luminance. Contrastingly, MWT distinguished two frequency bands at all luminances: high frequency (135 ± 6 Hz) time locked to the onset of early OPs and low frequency (82 ± 7 Hz), giving rise to early and late OPs. By 60 years, there was a consistent power reduction specific to the low-frequency band.

CONCLUSIONS

Age-related OP changes precede those seen with a- (photoreceptoral) and b-waves (postphotoreceptoral). In addition, MWT allows quantifying distinct low- and high-frequency oscillators in the human retina, which complement traditional OP analysis methods. The identification of an age-independent OP marker (light-adapted high frequency band) opens a new dimension for the screening of retinal degenerations and their impact on inner retina function.

Inner retina remodeling in a mouse model of stargardt-like macular dystrophy (STGD3)

Purpose. To investigate the impact of progressive age-related photoreceptor degeneration on retinal integrity in Stargardt-like macular dystrophy (STGD3). Methods. The structural design of the inner retina of the ELOVL4 transgenic mouse model of STGD3 was compared with that of age-matched littermate wild-type (WT) mice from 1 to 24 months of age by using immunohistofluorescence and confocal microscopy and by relying on antibodies against cell-type-specific markers, synapse-associated proteins, and neurotransmitters. Results. Müller cell reactivity occurred at the earliest age studied, before photoreceptor loss. This finding is perhaps not surprising, considering the cell's ubiquitous roles in retina homeostasis. Second-order neurons displayed salient morphologic changes as a function of photoreceptoral input loss. Age-related sprouting of dendritic fibers from rod bipolar and horizontal cells into the ONL did not occur. In contrast, with the loss of photoreceptor sensory input, these second-order neurons progressively bore fewer synapses. After rod loss, the few remaining cones showed abnormal opsin expression, revealing tortuous branched axons. After complete ONL loss (beyond 18 months of age), localized areas of extreme retinal disruptions were observed in the central retina. RPE cell invasion, dense networks of strongly reactive Müller cell processes, and invagination of axons and blood vessels were distinctive features of these regions. In addition, otherwise unaffected cholinergic amacrine cells displayed severe perturbation of their cell bodies and synaptic plexi in these areas. Conclusions. Remodeling in ELOVL4 transgenic mice follows a pattern similar to that reported after other types of hereditary retinopathies in animals and humans, pointing to a potentially common pathophysiologic mechanism.

The effect of bispectral index monitoring on end-tidal gas concentration and recovery duration after outpatient anesthesia

We performed this study to determine whether instituting monitoring of bispectral index (BIS) throughout an entire operating room would affect end-tidal gas concentration (as a surrogate for anesthetic use) or speed of recovery after outpatient surgery. Primary caregivers (n = 69) were randomly assigned to a BIS or non-BIS Control group with cross-over at 1-mo intervals for 7 mo. Data were obtained in all outpatients except for those having head-and-neck surgery. Mean end-tidal gas concentration and total recovery duration were compared by unpaired t-test. Overall, 469 patients (80%) received propofol for induction and sevoflurane for maintenance. This homogeneous group was selected for statistical analysis. Mean end-tidal sevoflurane concentration was 13% less in the BIS group (BIS, 1.23%; Control, 1.41%; P < 0.0001); differences were most evident when anesthesia was administered by first-year trainees. Mean BIS values were 47 in the BIS-Monitored group. Total recovery was 19 min less with BIS monitoring in men (BIS group, 147 min; Controls, 166 min; P = 0.035), but not different in women. We conclude that routine application of BIS monitoring is associated with a modest reduction in end-tidal sevoflurane concentration. In men, this may correlate with a similar reduction (11%) in recovery duration.

Trends in quality of anesthesia care associated with changing staffing patterns, productivity, and concurrency of case supervision in a teaching hospital

BACKGROUND

The authors used continuous quality improvement (CQI) program data to investigate trends in quality of anesthesia care associated with changing staffing patterns in a university hospital.

METHODS

The monthly proportion of cases performed by solo attending anesthesiologists versus attending-resident teams or attending-certified registered nurse anesthetist (CRNA) teams was used to measure staffing patterns. Anesthesia team productivity was measured as mean monthly surgical anesthesia hours billed per attending anesthesiologist per clinical day. Supervisory ratios (concurrency) were measured as mean monthly number of cases supervised concurrently by attending anesthesiologists. Quality of anesthesia care was measured as monthly rates of critical incidents, patient injury, escalation of care, operational inefficiencies, and human errors per 10,000 cases. Trends in quality at increasing productivity and concurrency levels from 1992 to 1997 were analyzed by the one-sided Jonckheere-Terpstra test.

RESULTS

Productivity was positively correlated with concurrency (r = 0.838; P<0.001). Productivity levels ranged from 10 to 17 h per anesthesiologist per clinical day. Concurrency ranged from 1.6 to 2.2 cases per attending anesthesiologist. At higher productivity and concurrency levels, solo anesthesiologists conducted a smaller percentage of cases, and the proportion of cases with CRNA team members increased. The patient injury rate decreased with increased productivity levels (P = 0.002), whereas the critical incident rate increased (P = 0.001). Changes in operational inefficiency, escalation of care, and human error rates were not statistically significant (P = 0.072, 0.345, 0.320, respectively).

CONCLUSIONS

Most aspects of quality of anesthesia care were apparently not effected by changing anesthesia team composition or increased productivity and concurrency. Only team performance was measured; the role of individuals (attending anesthesiologist, resident, or CRNA) in quality of care was not directly measured. Further research is needed to explain lower patient injury rates and increases in critical incident reporting at higher concurrency and productivity levels.

Cost-effective reduction of neuromuscular-blocking drug expenditures

BACKGROUND

Anesthetic drug expenditures have been a focus of cost-containment efforts. The aim of this study was to determine whether expenditures for neuromuscular-blocking agents could be reduced without compromising outcome, and to determine whether such a cost-effective pattern of neuromuscular blocker use could be sustained.

METHODS

Education, practice guidelines, and paperwork barriers were used to persuade anesthesiologists to substitute low-cost neuromuscular-blocking drugs (pancuronium or a metocurine-pancuronium combination) for a more costly neuromuscular-blocking drug (vecuronium). Neuromuscular-blocking drug use in all patients during a historical control period (6 months; n = 4,804) was compared with that during two consecutive 1-yr periods of intervention (n = 9,761/n = 10,695). Expenditures for vecuronium and for all neuromuscular-blocking drugs were compared for the control and intervention periods. The rate of complications related to neuromuscular-blocking drugs was determined by an ongoing continuous quality improvement program.

RESULTS

Vecuronium use decreased by 76% during the first and second yr of intervention, compared with the historical period (P < 0.01). The cost of neuromuscular-blocking drugs decreased by 31% (P < 0.01) and 47% (P < 0.01) for the first and second yr, respectively. The complication rate related to neuromuscular-blocking drugs was 0.081% in the historical period and 0.11% and 0.093% during the intervention periods (P = 0.29 and 0.41).

CONCLUSION

Practice guidelines, education, and paperwork barriers used together substantially reduced the expenditures for neuromuscular-blocking drugs for 2 yr without adversely affecting clinical outcome.

Hemodynamic response and change in organ blood volume during spinal anesthesia in elderly men with cardiac disease

Aging and disease may make the elderly patient with cardiac disease particularly susceptible to hypotension during spinal anesthesia. We studied 15 men, 59-80 y old, with histories of prior myocardial infarction (n = 9), congestive heart failure (n = 2), and/or stable myocardial ischemia (n = 11) given spinal anesthesia with 50 mg lidocaine in dextrose. Technetium-99m-labeled red blood cell imaging estimated left ventricular ejection fraction (EF) and changes in blood volume in the abdominal organs and legs. Arterial and pulmonary artery catheters provided hemodynamic measurements. Sensory block averaged T4 (range T1-10). Mean arterial pressure decreased 33% +/- 15% (SD) (P < 0.001), secondary to decreases in vascular resistance (SVR), -26% +/- 13% (P < 0.001) and cardiac output, -10% +/- 16% (P = 0.03). EF increased from 53% +/- 11% to 58% +/- 14% (P < 0.001) while left ventricular end-diastolic volume (LVEDV) decreased (-19% +/- 9%, P < 0.001). Blood volume increased in the legs (6% +/- 6%, P = 0.006), kidneys (10% +/- 9%, P < 0.001), and mesentery (7% +/- 5%, P 0.001) but not in the liver or spleen. Cardiac function was well maintained. We concluded that the primary mechanism of hypotension was a decrease in SVR, not cardiac output, despite the decrease in LVEDV.

Calcium channel blockers do not enhance increases in plasma potassium after succinylcholine in humans

STUDY OBJECTIVE

To determine whether chronic calcium channel blocker therapy exaggerates the rise in plasma potassium concentration ([K+]) after succinylcholine administration.

DESIGN

Prospective clinical study.

SETTING

University and Veterans Affairs hospitals.

PATIENTS

36 ASA physical status III and IV male patients: 21 patients taking chronic calcium channel blockers and 15 patients not receiving calcium channel blockers, all of whom were scheduled for inpatient surgical procedures with general anesthesia.

INTERVENTIONS

In all patients, anesthesia was induced with high-dose opioids plus a sedative-hypnotic, and intubation was facilitated with 1 to 1.5 mg/kg succinylcholine without nondepolarizing neuromuscular blocker pretreatment.

MEASUREMENTS AND MAIN RESULTS

Plasma [K+] was measured prior to induction and 1, 3, 5, 8, 11, and 15 minutes after succinylcholine was administered. A modest average peak rise of 0.5 mEq/L in plasma [K+] was observed, but there were no differences between patients who were or were not receiving calcium channel blockers.

CONCLUSIONS

Patients receiving chronic calcium channel blocker therapy are at no greater risk of hyperkalemia after succinylcholine than those not taking such medications.

A prospective study of intraoperative pulse oximetry failure

Since pulse oximetry is now an ASA standard for intraoperative monitoring, we sought to determine the intraoperative failure rate for this device. We prospectively evaluated the intraoperative failure rate of our pulse oximeters at the four University of Washington Hospitals (University of Washington Medical Center, Veterans Affairs Medical Center [VAMC], Children's Hospital and Medical Center, and Harborview Medical Center [HMC]) recorded from April 1989 to August 1989. We defined failure as the inability to obtain any oximetry reading for a cumulative period of more than 30 minutes during any anesthetic procedure after all equipment malfunctions had been eliminated. Our puse oximeters failed in 124 of 11,046 cases studied; this is a failure rate of 1.12%, which ranged from 0.56% at HMC to 4.24% at VAMC. The failure rate at VAMC (4.24%) was significantly higher than the other hospitals (p less than 0.001). Those cases associated with the pulse oximeter failure had the following characteristics: (1) an ASA status of 3 or higher, (2) lengthy operations, and (3) elderly patients. When the device did fail in a patient, it did not function for 32% of the mean anesthesia time. We conclude that the intraoperative use of the pulse oximetry can provide information about blood oxygen saturation in most patients. However, in approximately 1% of the patients we studied in the operating room, mechanically functioning pulse oximeters failed to provide readings of blood oxygen saturations during routine operative use.

Cystic fibrosis, vasoactive intestinal polypeptide, and active cutaneous vasodilation

The transmitter substance for the active cutaneous vasodilation that accompanies sweating during hyperthermia in humans is unknown. Hökfelt et al. (Nature Lond. 284: 515-521, 180) hypothesized that it is vasoactive intestinal polypeptide (VIP) that is cotransmitted with acetylcholine. Heinz-Erian et al. (Science Wash. DC 229: 1407-1408, 1985) reported that VIP innervation is sparse in the skin of persons with cystic fibrosis (CF). A corresponding attenuation of active vasodilation in these subjects would be evidence that VIP is involved in this effector mechanism of human thermor-regulation. Immunocytochemical analysis of skin biopsies from four men with CF confirmed that VIP innervation was sparse. We also analyzed immunoreactivity for calcitonin gene-related peptide (CGRP; normal), substance P (normal), and neuropeptide Y (low). VIP-immunoreactive Merkel cells were abnormal. Despite sparse VIP-immunoreactive innervation, our CF subjects' cutaneous vascular responses to hyperthermia were normal. Because VIP was not completely absent, this evidence is insufficient to rule out VIP as the vasodilator transmitter. However, the CGRP and substance P innervation we observed could mean that release of one or both of these peptides was the mechanism of the fully developed active cutaneous vasodilation.

Placement of esophageal stethoscope by acoustic criteria does not consistently yield an optimal location for the monitoring of core temperature

The esophageal stethoscope has evolved into a device for both acoustic and core temperature monitoring. To test whether routine placement according to acoustic criteria results in placement of the core temperature sensor in the region of contiguity between the esophagus and the heart, we determined the depth of placement electrocardiographically. All patients were undergoing nonthoracic elective operations requiring general anesthesia and tracheal intubation. First, we established that different observers selected the same esophageal depth within +/- 1 cm electrocardiographically, using the criterion of a symmetric biphasic P wave of maximal amplitude (7 patients). Then, in 30 more patients, we compared routine acoustic placements with the depths of the maximal-amplitude biphasic P wave. Stethoscopes placed according to acoustic criteria were within +/- 3 cm of P-wave depths in 15 of 30 patients. In the remaining patients, measured discrepancies ranged up to 13.5 cm. We conclude that the prevailing stethoscope design, with a thermistor at the tip, below the acoustic window, does not ensure placement of the thermistor within the optimal region for monitoring of core temperature. A modification in design that would take advantage of the reliability of electrocardiographic positioning is suggested.

EEG Suppression and Increased Blood-Brain Barrier Permeability Following Intracarotid Injection of Iothalamate Meglumine (Conray) in Dogs

Over a 2-year period we observed three cases of unilateral suppression of the electroencephalogram (EEG) lasting from 45 s to 4 min following intracarotid injection of 60% iothalamate meglumine (Conray) for intraoperative carotid angiography postendarterectomy. As a result of these cases we undertook studies in 11 dogs anesthetized with isoflurane to examine causes of EEG suppression following intracarotid contrast medium injection. In group 1 (n = 6) cerebral blood flow (CBF), the cerebral metabolic rate for oxygen (CMRO2), EEG activity, and permeability of the blood-brain barrier (BBB) were determined. In group 2 (n = 5) cerebrospinal fluid (CSF) pressure, EEG activity, and BBB permeability were determined. Intracarotid injection of 5 ml of 60% Conray was associated with unilateral EEG suppression and increased BBB permeability in 1 of 11 dogs. Injection of contrast material caused no change in CBF or CMRO2 and caused a statistically significant but physiologically unimportant increase of CSF pressure (from 12 +/- 1 to 16 +/- 1 cm H2O, mean +/- SEM). It is concluded that EEG suppression following intracarotid injection of Conray is a rare event. It seems unlikely that EEG suppression resulted from cerebral ischemia or hypoxia, but rather was associated with increased BBB permeability. Increased BBB permeability likely was caused by the osmotic effect of Conray and not by hypoxic-ischemic microvascular injury or loss of autoregulation of CBF.

Microcomputer-based data acquisition system for clinical research

We have described a computerized data acquisition system for clinical investigation that can record over fifty physiologic variables from up to twenty-four electronic monitors. The information is acquired by a personal computer using RS-232C serial communications and analog-to-digital conversion. In its present configuration the system records information from a Spacelabs 500 series physiologic monitor, Hewlett-Packard physiologic monitor with the Careport computer interface, SARA mass spectrometer, Nellcor pulse oximeter, Neurotrac processed EEG, Lawrence cardiac output monitor, Hewlett-Packard capnometer, and Bourns spirometer. The software can be easily modified to accommodate other physiologic monitors. The system records parameter or waveform information and writes the data into a file that can be accessed by commercially available graphical and statistical packages. The data acquisition system is easy to use, transportable, and inexpensive.

Does acute hypoxemia blunt sympathetic activity in hyperthermia?

Sympathetic alpha-adrenergic function is depressed by hypoxemia per se; does addition of another sympathoexcitatory stimulus elicit normal responses in other sympathetic effector pathways? We activated by hyperthermia four sympathetic pathways: alpha-adrenergic [norepinephrine (NE) release], beta-adrenergic [plasma renin activity (PRA)], cholinergic (sweating), and peptidergic (active vasodilation). In the first test, five normothermic men were exposed to hypoxemia for 10 min (control), then hypoxemia plus heat for 30 min, and then heat with normoxia for 8-10 min over a continuous 48- to 50-min period. Heating was controlled with a water-perfused suit. Time courses and magnitudes of heat-induced increments in body temperature, forearm blood flow, and sweat rate were normal during hypoxemia and unaffected by switching to normoxia. Hypoxemia exaggerated increases in plasma NE, epinephrine, PRA, and heart rate but had no additional effects on blood pressure. In a second 50-min test (2 men) with normoxic control (10 min), heating plus normoxia (20 min), and heating plus hypoxemia (20 min), effects of hypoxemia on all variables were as in the first test. Thus, acute moderate hypoxemia did not blunt active cutaneous vasodilation or sweating and exaggerated increases in catecholamines and heart rate, indicating maintained peripheral autonomic function.

Effect of spontaneous sighs on arterial oxygenation during isoflurane anesthesia in humans

The presence, frequency, and volume of spontaneous sighs was evaluated in 21 (ASA 1-2) supine patients aged 44 +/- 15.2 (SD) yr, during isoflurane-nitrous oxide anesthesia. Before induction the inspiratory capacity of each patient was determined. After induction of anesthesia and tracheal intubation patients breathed spontaneously except for three manual inflations to each patient's predetermined inspiratory capacity at the beginning and end of surgery. Arterial blood gas tensions were measured before and 5 min after each set of mechanical deep breaths and each hour during surgery, the mean duration of which was 2 +/- 0.09 hr. Spontaneous sighs occurred in 13 of 21 patients. The average frequency was 6 +/- 4 sighs/hr. At FIO2 = 0.5, nonsighing patients had an initial PaO2 of 229 +/- 59 mm Hg and sighers had an initial PaO2 of 162 +/- 57 mm Hg (P less than 0.05). Arterial oxygen did not change in sighing patients during the course of surgery, while in nonsighing patients the PaO2 decreased from the initial value of 229 +/- 60 mm Hg to 170 +/- 63 mm Hg (P less than 0.05). Mechanical deep breaths administered at the end of surgery produced no improvement in oxygenation in either sighers or nonsighers. The presence or absence of sighs did not correlate with PaO2 or PACO2. Though the results suggest that spontaneous sighs in some patients may function to help maintain arterial oxygenation, all patients maintained their PaO2 while breathing spontaneously under general anesthesia in the supine position.

Respiratory effects of nalbuphine and butorphanol in anesthetized patients

A double-blind, randomized study was conducted in 16 patients who were anesthetized with 50% nitrous oxide in oxygen and given either 0.17 mg/kg butorphanol or 0.86 mg/kg nalbuphine, and whose respiratory depression was assessed by the response of minute ventilation to increasing carbon dioxide concentrations. The slopes of the carbon dioxide ventilatory response curves [delta VE/delta PCO2(L.min-1 X %CO2(-1)] were 7.45 +/- 1.17 with nalbuphine and 2.42 +/- 0.56 with butorphanol. Butorphanol caused significantly (P less than 0.025) greater respiratory depression than nalbuphine. The results of this study caution against the indiscriminate use of butorphanol in the perianesthetic setting.

Transesophageal Doppler scanning versus thermodilution during general anesthesia. An initial comparison of cardiac output techniques

Measurement of cardiac output has become an essential feature of anesthetic management of patients with cardiac disease requiring operation. Thermodilution by way of a Swan-Ganz catheter is the current popular technique for cardiac output determination. Unfortunately, this method is costly and has an associated irreducible morbidity rate and has, in rare instances, resulted in death. The suprasternal ultrasonographic Doppler technique has shown promise for measuring cardiac output noninvasively; however, it is too cumbersome for continuous intraoperative use. In an effort to overcome this limitation, the esophageal stethoscope was modified to accept a Doppler probe. Herein, we have reported an initial comparison of transesophageal Doppler scanning and thermodilution in 23 adult men during general anesthesia. The average difference between thermodilution and descending cardiac output was 0.16 +/- 0.81 liters/min. The correlation between thermodilution and descending cardiac output increased with operator experience. In the last 13 patients, there was an average correlation of 0.85. After the equipment was mastered and improvements in design were made, descending cardiac output had a high correlation with thermodilution and appeared to track the dynamic changes during general anesthesia.

Unaltered norepinephrine-heart rate relationship in exercise with exogenous heat

We measured plasma norepinephrine (NE) concentration, an index of sympathetic nervous activity, and epinephrine (E), an index of adrenal medulla activity, in six normal young men during mild to severe exercise, with and without superimposed heat stress. The primary objective was to observe whether the normally close relationship between heart rate and log NE concentration in upset when heart rate at a given work load is increased by heat stress. Exercise, beginning at 50 W, was graded in 50-W increments lasting 10 min each up to 200 W, which lasted 5-10 min. Each subject went through the protocol twice, once with skin temperature kept low by a water-perfused suit and then with skin temperature raised to 38 degrees C. Exogenous heart stress raised log circulating NE concentration in proportion to the rise in heart rate at a given work load so that the usual relationship between these variables, previously observed during other stresses, was preserved. In contrast to some other stresses, heat stress had no added effect on E concentration, indicating that this stress during exercise raises sympathetic neural activity (as reflected in the rise in NE) without stimulating additional adrenal release of E.

Propranolol reduces bupivacaine clearance

Propranolol reduces the clearance of lidocaine by both reducing hepatic blood flow and inhibiting lidocaine metabolism. The authors investigated the possibility that propranolol reduces the clearance of bupivacaine as well. Bupivacaine, 30-50 mg, was administered intravenously to six normal human volunteers, over 10-15 min on two occasions, at least 2 weeks apart. Propranolol, 40 mg orally every 6 h, was used on one occasion, beginning 24 h prior to the bupivacaine administration. The sequence of the sessions was randomized. Twenty-two venous blood samples were obtained over 36 h in order to determine bupivacaine clearance, terminal elimination rate constant, and volume of distribution. All subjects experienced mild CNS toxicity, consisting of tinnitus, facial tingling, or subtle visual disturbances, associated with peak venous plasma concentrations of 0.81 to 2.7 micrograms/ml. Mean bupivacaine clearance was 0.33 +/- 0.12 l/min for the control session and 0.21 +/- 0.12 l/min during propranolol use, a significant 35% reduction (P less than 0.01). The terminal elimination rate constant (beta) was 0.27 +/- 0.16 h-1 for the control session and 0.14 +/- 0.069 h-1 with propranolol (P less than 0.05); terminal elimination half-lives were 2.6 and 4.9 h, respectively. Volume of distribution was unchanged. Because bupivacaine clearance should be relatively insensitive to hepatic perfusion, it appeared that propranolol caused a substantial inhibition of bupivacaine metabolism at the level of the hepatocyte. These data suggest that concomitant use of propranolol could result in the accumulation of a toxic concentration of bupivacaine.

Plasma renin activity and forearm blood flow in paraplegic humans

We recently found that paraplegic humans respond to hyperthermia with subnormal increase in skin blood flow (SkBF), based on measurements of forearm blood flow (FBF). Is this inhibition of SkBF a defect in thermoregulation or a cardiovascular adjustment necessary for blood pressure control? Since high resting plasma renin activity (PRA) is found in unstressed individuals with spinal cord lesions and since PRA increases during hyperthermia in normal humans, we inquired whether the renin-angiotensin system is responsible for the attenuated FBF in hyperthermic resting paraplegics. Five subjects, 28-47 yr, with spinal transections (T1-T10), were heated in water-perfused suits. Blood samples for PRA determinations were collected during a control period and after internal temperature reached approximately 38 degrees C. Some subjects with markedly attenuated FBF had little or no elevation of PRA; those with the best-developed FBF response exhibited the highest PRA. Clearly, circulating angiotensin is not the agent that attenuates SkBF. Rather, increased activity of the renin-angiotensin system may be a favorable adaptation that counters the locally mediated SkBF increase in the lower body and thus allows controlled active vasodilation in the part of the body subject to centrally integrated sympathetic effector outflow.

Sweat rate vs. forearm blood flow during lower body negative pressure

Skin blood flow is inhibited when hyperthermia and added hypovolemic stresses are superimposed. We tested the hypothesis that part of this inhibition is a reduced drive for cutaneous active vasodilatation (AVD) with sweat rate (SR) taken as an indirect measure of the efferent drive for cutaneous AVD. We also inquired whether SR itself changes with redistribution of blood volume. Six healthy supine men were subjected to lower body negative pressure (LBNP) after heating in water-perfused suits increased esophageal temperatures (Tes) to a mean of 37.2 degrees C and at least doubled SR and forearm vascular conductance (FVC). Heating continued throughout LBNP and recovery. Sweat rate did not decrease with LBNP onset, although SR-Tes slopes during LBNP were reduced 28% from control. In four subjects the SR-Tes slope did not recover when LBNP was discontinued. These observations suggest that SR is not an effector of the low-pressure baroreflex. In contrast to SR, FVC abruptly fell 22% at the onset of LBNP. Thereafter, FVC-Tes slopes near zero or less occurred. The major effector for FVC inhibition with LBNP appears to be the neural vasoconstrictor system. A minor component due to reduced drive for cutaneous AVD probably occurs as well.

Caudal anesthesia with lidocaine or bupivacaine: plasma local anesthetic concentration and extent of sensory spread in old and young patients

Continuous caudal peridural anesthesia with 2% lidocaine (6 mg/kg) or 0.75% bupivacaine (2.2 mg/kg), both with epinephrine 1:200,000, was studied in two groups of male patients, younger than 40 or older than 55 yr old, respectively. Patients receiving lidocaine in the younger group (n = 6) were 32 +/- 5.2 (mean +/- SD) yr old and weighed 75 +/- 12 kg, while those in the older group (n = 16) were 66 +/- 5.3 yr old and weighed 72 +/- 8.2 kg. Patients receiving bupivacaine in the respective groups were 27 +/- 7.0 yr old (n = 5), and 76 +/- 10 kg compared to 69 +/- 10 yr (n = 14) and 75 +/- 10 kg. Anesthesia was satisfactory in all patients. Extent of sensory anesthesia, peak plasma lidocaine or bupivacaine concentrations, and area under the plasma concentration-time curves were independent of age. No local anesthetic toxicity was observed and peak drug concentrations were below those commonly associated with toxicity.

Attenuated skin blood flow response to hyperthermia in paraplegic men

To clarify how skin and internal temperatures interact in control of skin blood flow, five male paraplegic subjects (lesions at the level of thoracic vertebrae 1-11) (29-47 yr old) were heated in water-perfused suits to elevate oral temperature (To) 1-1.5 degrees C. In part I only the insensate skin was heated; sensate skin was kept at 32-34 degrees C. No appreciable elevation of forearm blood flow (FBF) or sweating occurred, even with To at 38 degrees C. In part II the suit was applied to the whole body so that skin temperature was 40 degrees C, except for one arm that remained at 32-34 degrees C for FBF measurement. Sweating was noted above the lesion in all but one subject. FBF increased in all subjects but was far below levels previously reported for hyperthermic normal men; also, thresholds appeared elevated. To the extent that effector connections are intact, attenuated FBF response implies that either 1) some vasoconstrictor bias associated with cardiovascular regulation is active or 2) thermoregulatory effector outflow is diminished. If the latter is true, it follows that the effector outflow reduction relates to diminished afferent input. But the component of the effector outflow contributed by peripheral thermoreception is small; thus these findings may indicate that what is lacking in the afferent input is central thermoreception from below the lesion, possibly from the spinal cord itself.

Cutaneous vascular response to exercise and acute hypoxia

Six normal young men were studied during 50 min of moderate exercise (100-137 W) that included one 15-min (protocol 1) or two 10-min periods of breathing 11-12% O2 (in N2) (protocol 2). Absolute work intensity was kept constant for each subject, but relative severity increased during hypoxia owing to reduction in maximum O2 uptake. Our question was whether hypoxia causes cutaneous vasoconstriction; this in turn should cause a rise in esophageal temperature (Tes) and a shift in the forearm skin blood flow (SkBF)-Tes relationship. In all subjects forearm blood flow (FBF) (venous occlusion plethysmography) rose throughout exercise and Tes tended to stabilize. Neither 10- nor 15-min periods of hypoxia caused systematic changes in FBF or Tes or their relationship to each other. We conclude that hypoxia equivalent to that incurred at 4,500-5,000 m does not significantly alter the short-term regulation of SkBF and body temperature during moderate exercise. Net cutaneous vasoconstriction is not elicited by arterial chemoreflexes under these conditions.

Splanchnic vasoconstriction in heat-stressed men: role of renin-angiotensin system

We conducted a two-part study to determine whether the renin-angiotensin system contributes to the rise in splanchnic vascular resistance (SVR) during heat stress (rectal temperature was raised 1 degree C). In experiment 1 (control) seven men on a normal salt diet were directly heated (water-perfused suits) for 40-50 min. Arterial pressure (85 Torr) was unchanged; plasma renin activity (PRA) rose from 102 to 239 ng angiotensin I.100 ml-1.3 h-1; and SVR increased 73% (from 63 to 109 units). Experiment 2 was a repetition of experiment 1 on the same subjects, except that propranolol (10 mg iv) was given at the onset of heating to block renin release. Propranolol attenuated the rise in heart rate and reduced mean arterial pressure from 82 to 72 Torr; it blocked the rise in PRA with heating in two subjects, reduced it in three, but increased it in two. Although changes in SVR paralleled those in PRA in three subjects, SVR still rose 60% (from 58 to 99 units) after PRA rise was blocked. In both experiments, plasma norepinephrine concentration rose indicating increased sympathetic nervous activity. During mild heat stress, increased PRA is not a major factor in the increase of SVR.

Vasomotor control in healed grafted skin in humans

Do the vasomotor functions unique to skin recover in a skin graft? To determine whether locally mediated vasodilation and active reflex vasodilation recovery, we applied direct heating and whole-body heating, respectively. Also, presence of sympathetic cutaneous vasoconstriction was tested with application of lower body negative pressure (LBNP) during local heating. Subjects were six men who had been severely burned. Forearm blood flow (FBF) was recorded (venous occlusion plethysmography) in regions with healed split-thickness circumferential grafts. All subjects responded normally to local heating of the forearm (irrigation with 42 degrees C water). All but one showed cutaneous vasoconstriction in response to LBNP. Three subjects responded normally to whole-body heating with water-perfused suits (oral temperature elevation approximately 1.5 degrees C); two subjects had attenuated responses. No active vasodilation was normal cutaneous vasomotor functions return in (or under) split-thickness skin grafts, recovery and associated thermoregulatory function may be attenuated or absent, perhaps in relation to the survival of dermis.

Absence of active cutaneous vasodilation associated with congenital absence of sweat glands in humans

In the rare syndrome, hereditary anhidrotic ectodermal dysplasia (AED), sweat glands are congenitally absent. Assuming normal vasculature and normal central mechanisms, presence or absence of active cutaneous vasodilation (AVD) in hyperthermic subjects with AED critically tests the hypothesis that AVD is a consequence of sudomotor activity. Three men with full expression of the syndrome and a woman who is mosaic were heated in water-perfused suits until oral temperature was 1.4-1.7 degrees C above control. The men showed no sweat gland imprints on iodine-treated paper nor significant elevation in forearm blood flow (FBF, determined plethysmographically). In the woman, we observed sweat gland activity, approximately 9 and 22 glands/cm2, on the right and left side, respectively, and vasodilation, slight on the right and more on the left. Cutaneous vasoconstriction in response to negative pressure applied to the lower body was observed (3 subjects) and local FBF increased in response to local heating (2 subjects). Therefore, in AED, with apparently normal cutaneous vasculature and sympathetic innervation, AVD is absent as well as sweat glands.

Blockade of the pressor response to muscle ischemia by sensory nerve block in man

Differential nerve block from peridural anesthesia was used to determine a) if the pressor response to muscle ischemia in man is caused by stimulation of small sensory nerve fibers and b) if these fibers contribute to cardiovascular-respiratory responses during dynamic exercise. Four men exercised at 50-100 W for 5 min. Muscle ischemia and a sustained pressor response were produced by total circulatory occlusion of both legs beginning 30 s before the end of exercise and continuing for 3 min postexercise. During regression of full motor and sensory block, motor strength recovered while sensory block continued; the pressor response was blocked as long as sensory anesthesia persisted (two subjects). During blockade of the pressor response, cardiovascular-respiratory responses to exercise gradually returned from augmented to normal (preblock) levels. Sensory blockade was incomplete in two subjects and the pressor response was not fully blocked. We conclude that stimulation of small sensory fibers during ischemia elicits the pressor response, but that these fibers appear not to contribute to cardiovascular-respiratory responses during mild dynamic exercise with adequate blood flow.

Cardiovascular responses to muscle ischemia in man--dependency on muscle mass

We sought to determine whether the pressor response to exercise-induced muscle ischemia is related to the mass of tissue rendered ischemic. Six men repeatedly exercised for 5 min at a fixed load between 75 and 150 W (bicycle ergometer). Thirty seconds before the end of exercise, circulation to one calf, two calves, one leg, and two legs was arrested with pneumatic cuffs in successive tests with 15-min recovery periods interspersed. Each occlusion was maintained until the 3rd min of exercise recovery. During postexercise occlusion we observed 1) mean arterial pressure (MAP) was elevated in proportion to the mass of ischemic muscle, 2) forearm blood flow (FBF) was elevated during the overlap of occlusion with exercise but did not show a uniform response during the following 3 min of occlusion--either vasoconstriction or vasodilation occurred, 3) heart rate (HR) was elevated only when two legs were occluded, and 4) occlusion did not affect ventilation or endtidal CO2. We conclude that the ischemic pressor response is muscle mass-dependent. Our findings suggest that the baroreflex alters peripheral vascular resistance so as to aid in the maintenance of elevated MAP.