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Biomedical subjects

G Hertz

Publications and source records attributed to G Hertz.

13 recordsLinked to original sources
PubMed1995

Developmental trends of sleep-disordered breathing in Prader-Willi syndrome: the role of obesity.

Polysomnographic recordings of 43 children and adults with Prader-Willi syndrome (PWS) were inspected and classified into 5 age groups. The effect of age and body mass index (BMI) on measures of breathing, oxygen saturation, and sleep efficiency were analyzed. Body mass index (BMI) increased significantly between early childhood and preadolescent groups. Subjecting the data to analysis of variance showed an overall significant effect of BMI but no age effect on breathing parameters and oxygen saturation. Increased BMI was associated with decreased oxygen saturation and with higher apnea/hypopnea index. Sleep efficiency index was significantly lower in adults than in young children, preadolescent, and adolescent groups. These findings emphasize the role of obesity in the development of sleep-related breathing abnormalities and nocturnal oxygen desaturation in patients with PWS.

Adolescent↗
PubMed1995

Comparison of a frequency-based analysis of electroencephalograms (Z-ratio) and visual scoring on the multiple sleep latency test.

In a sample of multiple sleep latency test naps following nocturnal polysomnograms from a group of 13 patients of varying ages and diagnoses, we compared a computer-derived electroencephalographic (EEG) measure (z-ratio) with standard visual sleep stage scoring. In this clinical population, z-ratio scoring agreed with human scorers approximately 80% of the time when determining sleep versus wake in 30-second epochs. These results show that a single, objectively quantifiable value derived from a single channel of EEG can distinguish between sleep and wakefulness (as defined by Rechtschaffen and Kales) with at least a moderate degree of precision. When refined, the z-ratio method might be of use as the basis for a new sleep scoring system, particularly where an accurate determination of sleep onset is required.

Adolescent↗
PubMed1994

Premature infants in car seats: effect of sleep state on breathing.

Previous studies have shown that premature infants may be at risk for hypoxemia and bradycardia when placed in standard car seats. However, the relationship of such breathing abnormalities to sleep state have not been studied. The purpose of the present study was to investigate the effect of car seat positioning on respiratory patterns in preterm infants during sleep and to evaluate their relationship to sleep state. Complete polysomnography, including sleep and breathing parameters, was performed on twenty-eight premature infants. Each infant was randomly assigned to the car seat or prone (crib) position for the first recording period. Following the recording of at least two sleep cycles, the position was reversed. The percentage of active and quiet sleep was calculated and breathing parameters were measured. In the car seat, the infants spent significantly more time in active sleep and less time in quiet sleep than in the prone position, of the respiratory parameters, periodic breathing (PB) was significantly higher in the car seat. The presence of at least one abnormal breathing events (bradycardia, desaturation, PB apnoea) was also significantly higher in the car seat. An analysis of variance (ANOVA) of PB revealed significant sleep-state effect (active vs. quiet sleep), but no significant condition or interaction effects, indicating that PB was more frequent in active sleep regardless of the sleeping condition. It is concluded that increased active sleep in the car seat condition, rather than the positioning of the infant in the seat per se, may account for the increase in periodic breathing and possibly other breathing abnormalities reported in car seats.

Journal Article↗
PubMed1993

Sleep and breathing patterns in patients with Prader Willi syndrome (PWS): effects of age and gender.

Patients with Prader Willi syndrome (PWS) often complain of daytime hypersomnolence. Because of reported daytime sleepiness and high prevalence of morbid obesity, these patients have been considered at risk for sleep related disordered breathing, but polysomnographic studies have been limited. We evaluated sleep and breathing polysomnographically in 24 PWS patients including 15 adults and 9 children. All adult patients completed MSLT testing on the day following the nocturnal sleep study. Both adult and children groups showed little or no sleep apnea, but REM related oxygen desaturation was quite common, its severity significantly correlated with increased obesity. Sleep patterns in both groups showed abnormal REM sleep cycles with variable REM latency (at times significantly shortened) and fragmented REM sleep with multiple brief REM periods. REM sleep abnormalities were still present in some patients without REM related desaturation. As a group, patients with PWS demonstrated pathological somnolence as measured by MSLT, which correlated with nocturnal sleep efficiency but not with nocturnal REM latency. It is hypothesized that the abnormal sleep findings in PWS reflect an underlying hypothalamic dysfunction characteristic of this syndrome.

Adolescent↗
PubMed1993

Sleep in the elderly patient.

Sleep problems in the elderly are extraordinarily common. The authors discuss normal sleep, changes in sleep with normal aging, and sleep disorders in the elderly, focusing on sleep-disordered breathing. In addition, nocturnal myoclonus and rapid-eye movement behavior disorder are reviewed.

Aged↗
PubMed1992

Splicing signals in Drosophila: intron size, information content, and consensus sequences.

A database of 209 Drosophila introns was extracted from Genbank (release number 64.0) and examined by a number of methods in order to characterize features that might serve as signals for messenger RNA splicing. A tight distribution of sizes was observed: while the smallest introns in the database are 51 nucleotides, more than half are less than 80 nucleotides in length, and most of these have lengths in the range of 59-67 nucleotides. Drosophila splice sites found in large and small introns differ in only minor ways from each other and from those found in vertebrate introns. However, larger introns have greater pyrimidine-richness in the region between 11 and 21 nucleotides upstream of 3' splice sites. The Drosophila branchpoint consensus matrix resembles C T A A T (in which branch formation occurs at the underlined A), and differs from the corresponding mammalian signal in the absence of G at the position immediately preceding the branchpoint. The distribution of occurrences of this sequence suggests a minimum distance between 5' splice sites and branchpoints of about 38 nucleotides, and a minimum distance between 3' splice sites and branchpoints of 15 nucleotides. The methods we have used detect no information in exon sequences other than in the few nucleotides immediately adjacent to the splice sites. However, Drosophila resembles many other species in that there is a discontinuity in A + T content between exons and introns, which are A + T rich.

Animals↗
PubMed1992

Sleep in normal late pregnancy.

Twelve women in their third trimester of pregnancy and 10 age-matched nonpregnant controls underwent complete polysomnography for one night in the laboratory. Seven of the original women returned for a second study 3-5 months postpartum. During late pregnancy, women showed increased wake after sleep onset (WASO) and a lower sleep efficiency in comparison with the control group. The percentage of rapid eye movement (REM) sleep was significantly decreased and the percentage of stage 1 significantly increased compared to the nonpregnant group. At 3-5 months postpartum, a significant reduction in WASO and increased sleep efficiency were noted. However, only a slight increase was noted in REM sleep during the postpartum period compared to the prepartum period. The most frequent sleep complaints in the pregnant group were restless sleep, low back pain, leg cramps and frightening dreams. In summary, in accordance with their complaints, women in their third trimester demonstrated polysomnographic patterns of sleep maintenance insomnia.

Adult↗
PubMed1992

Respiration during sleep in pregnancy.

Several changes in maternal physiology may profoundly alter sleep, especially during late pregnancy. Any condition that causes maternal hypoxemia will be worsened during sleep, particularly in the supine position. Although high circulating levels of progesterone increase respiratory drive during sleep, in at least some women this protective mechanism is insufficient to prevent sleep-disordered breathing and hypoxemia. The true incidence of sleep-disordered breathing during pregnancy remains unknown. Although many women report sleep disturbance during pregnancy, those with severe snoring, observed irregular breathing with sleep, or excessive daytime somnolence should be referred for clinical polysomnography. With few data thus far available, nasal CPAP would appear to be the treatment of choice. Given the possible consequences of sleep apnea for fetal outcome, any significant sleep-disordered breathing is probably an indication for treatment.

Female↗
PubMed1989

Night backache in pregnancy. Hypothetical pathophysiological mechanisms.

One hundred women responded to a questionnaire dealing with night backache during pregnancy. All the women were in the second half of their pregnancy. Sixty seven per cent of the women reported discomfort and/or backache during the night. We hypothesize that hypervolemia combined with obstruction of the inferior vena cava, caused by the enlarging uterus, is the underlying pathomechanism leading to night backache. Patients with inadequate venous collateral circulation may develop excessive pressure within the venous system, the vertebral bodies and overdistension of venous channels distal to the occluded zone. These changes may lead to hypoxemia, metabolic disturbances, irritation of unmyelinated nerves and result in night backache.

Back Pain↗
PubMed1979

Increased sleep motility and respiration rates in combat neurotic patients.

Noctural rates of body movements and respiratory rates were studied in 11 combat neurosis patients and 9 normal controls. Patients had significantly higher rates of body movements in sleep stage 2, and significantly higher respiratory rates in NONREM sleep and in the second REM period than normals. In patients the rates of body movements were positively correlated with sleep efficiency indices. Since some of these patients were suspected of having non-restorative sleep syndrome, it is suggested that increased sleep motility and autonomic activity might be related to this sleep disorder.

Adult↗
PubMed1977

Cone signals in the cat's retina.

1. The discharges of ganglion cells in the cat's retina were recorded under conditions intended to isolate the cone system.2. Stiles' two-colour threshold technique permitted the photopic system to be studied when at its highest sensitivity. The absolute sensitivity of a ganglion cell, expressed in equivalent photons of lambda(max) at the cornea per impulse discharged, was about 2500 times less when driven by cones than when driven by rods. This ratio improves to around 200 when allowance is made for the much smaller fraction absorbed by cones of photons incident on the cornea.3. The number of extra impulses discharged in response to a brief flash was approximately proportional to the number of photons in the flash, up to a limit.4. There was a region in the middle of the receptive field within which the area of a test spot and its illumination for threshold varied inversely. A flash extending over the peripheral part of the receptive field raised threshold above its minimum, presumably as a result of surround antagonism. Assessed from area-threshold curves, the balance of centre-surround antagonism in the photopic receptive field did not seem to depend upon background illumination.5. The threshold for a small (0.2 degrees ) flash confined to the middle of the receptive field was independent of background illumination until the background exceeded a particular level, the ;dark light' (I(o)). In different units this ranged about a mean of 7.89 log photons (560 nm equivalent) deg(-2) sec(-1). For backgrounds that exceeded I(o), threshold followed approximately Weber's law up to the highest illuminations that could be produced.6. With test flashes that filled the centre of the receptive field, the Weber fraction (test flash illumination/background illumination) in some units fell below 1%.7. Changes in the time course and latency of response accompanied the changes in sensitivity caused by alterations in background illumination. Responses of both X- and Y-cells became more transient and faster.8. The loss of sensitivity to a test flash brought about by a steady background light depended upon the size of that light. Sensitivity varied inversely with background area within a central region that matched closely the summing area for test flashes.

Action Potentials↗
PubMedDate not supplied

Nocturnal low back pain in pregnancy: polysomnographic correlates.

Thirteen women in late stages of pregnancy underwent a polysomnographic study. Eight women (61%) complained of mild nocturnal back pain or back discomfort. Five women (39%) did not complain of nocturnal back pain. The two groups did not differ in total bed time, total sleep time, sleep latency, and wake after sleep onset (WASO). A significant decrease in rapid eye movement (REM) sleep and an increase in stage 2 were observed in the pain group. The same group had a statistically significant decrease in the basal O2 saturation level. The pain group also spent a longer time sleeping in the supine position. We hypothesize that a prolonged stay in the supine position leads to obstruction of the vena cava. In the presence of inadequate collateral circulation, increased pressure and venostasis in combination with a decrease in basal oxygen saturation may lead to hypoxemia, compromise the metabolic supply of the neural structures, and result in pain. It appears, therefore, that the vascular system plays an important role in the pathogenesis of pain. The role played by the disturbed sleep architecture in the production of pain remains to be established. It is possible that the changes observed in sleep architecture result from pain rather than contribute to pain production.

Adult↗