PubMed Health⌕ Search

Biomedical subjects

Gregory A L Davies

Publications and source records attributed to Gregory A L Davies.

17 recordsLinked to original sources
PubMed2006

Auditory processing deficits in growth restricted fetuses affect later language development.

An increased risk for language deficits in infants born growth restricted has been reported in follow-up studies for more than 20 years, suggesting a relation between fetal auditory system development and later language learning. Work with animal models indicate that there are at least two ways in which growth restriction could affect the development of auditory perception in human fetuses: a delay in myelination or conduction and an increase in sensorineural threshold. Systematic study of auditory function in growth restricted human fetuses has not been reported. However, results of studies employing low-risk fetuses delivering as healthy full-term infants demonstrate that, by late gestation, the fetus can hear, sound properties modulate behavior, and sensory information is available from both inside (e.g., maternal vascular) and outside (e.g., noise, voices, music) of the maternal body. These data provide substantive evidence that the auditory system is functioning and that environmental sounds are available for shaping neural networks and laying the foundation for language acquisition before birth. We hypothesize that fetal growth restriction affects auditory system development, resulting in atypical auditory information processing in growth restricted fetuses compared to healthy, appropriately-grown-for-gestational-age fetuses. Speech perception that lays the foundation for later language competence will differ in growth restricted compared to normally grown fetuses and be associated with later language abilities.

Child↗
PubMed2006

Phasic menstrual cycle effects on the control of breathing in healthy women.

This study examined the effects of menstrual cycle phase on ventilatory control. Fourteen eumenorrheic women were studied in the early follicular (FP; 1-6 days) and mid-luteal (LP; 20-24 days) phase of the menstrual cycle. Blood for the determination of arterial PCO(2) (PaCO(2)) , plasma strong ion difference ([SID]), progesterone ([P(4)]), and 17beta-estradiol ([E(2)]) concentrations were obtained at rest. Subjects performed a CO(2) rebreathing procedure that included prior hyperventilation and maintenance of iso-oxia to evaluate central and peripheral chemoreflex, and nonchemoreflex drives to breathe. Resting PaCO(2) and [SID] were lower; minute ventilation (V (E)), [P(4)] and [E(2)] were higher in the LP versus FP. Within the LP, significant correlations were observed for PaCO(2) with [P(4)], [E(2)] and [SID]. Menstrual cycle phase had no effect on the threshold or sensitivity of the central and/or peripheral ventilatory chemoreflex response to CO(2). Both (V (E)) and the ventilatory response to hypocapnia (representing nonchemoreflex drives to breathe) were approximately 1L/min greater in the LP versus FP accounting for the reduction in PaCO(2) . These data support the hypothesis that phasic menstrual cycle changes in PaCO(2) may be due, at least in part, to the stimulatory effects of [P(4)], [E(2)] and [SID] on ventilatory drive.

Adult↗
PubMed2006

Cold pressor test protocol to evaluate cardiac autonomic function.

The primary objective of this study was to develop a cold pressor test (CPT) protocol to evaluate cardiac autonomic function. Secondary objectives were to assess CPT protocol reliability and to examine gender differences in response to orthostatic stress and the CPT. Healthy, normotensive men and women (n = 12 per group) completed 2 trials on different days in the left lateral decubitus and standing postures and during a 6 min CPT (hand immersion while seated). Measurements included R-R interval, blood pressure, ventilatory responses, spontaneous baroreflex sensitivity, and heart rate variability indices. During the CPT, blood pressure and the sympathetic nervous system (SNS) indicator increased significantly and low-frequency power, high-frequency power (normalized for tidal volume), and the parasympathetic nervous system (PNS) indicator decreased significantly. Standing caused significant increases in the SNS indicator and decreases in the R-R interval in both genders. The PNS indicator was higher in women than in men in the left lateral decubitus posture. The 6 min hand-immersion CPT provoked cardiac sympathetic activation and parasympathetic withdrawal; however, it is best suited to studies with a repeated measures design, as analysis of reliability suggests that responses are highly variable between individuals. Performing the CPT in the left lateral decubitus position may prevent vasovagal responses.

Adult↗
PubMed2006

Exercise in the prevention and treatment of maternal-fetal disease: a review of the literature.

Evidence-based guidelines indicate that regular prenatal exercise is an important component of a healthy pregnancy. In addition to maintaining physical fitness, exercise may be beneficial in preventing or treating maternal-fetal diseases. Women who are the most physically active have the lowest prevalence of gestational diabetes (GDM), and prevention of GDM may decrease the incidence of obesity and type 2 diabetes in both mother and offspring. However, few studies have investigated the effectiveness of exercise in delaying or preventing GDM in at-risk women, and exercise prescriptions that optimize outcomes for women with GDM are lacking. Physically active women are also less likely to develop pre-eclampsia, and we have proposed the following 4 mechanisms that may explain this protective effect: enhanced placental growth and vascularity, reduced oxidative stress, reduced inflammation, and correction of disease-related endothelial dysfunction. Exercise may also prevent reproductive complications associated with maternal obesity. Obesity increases the risk of infertility and miscarriage, and weight loss programs that incorporate diet and exercise are a cost-effective fertility treatment that may also reduce the probability of obesity-related complications during pregnancy. Regular exercise following conception may prevent excessive gestational weight gain and reduce post-partum weight retention.

Algorithms↗
PubMed2006

Physicochemical analysis of acid-base responses to prolonged moderate exercise in late gestation.

Stewart's physicochemical approach was employed to investigate the safety of an average recreational and occupational activity (prolonged moderate exercise) on maternal acid-base homeostasis. The responses of 10 healthy, physically active pregnant women (PG, gestational age 34-38 weeks) were compared with those of 10 non-pregnant female controls (CG). Subjects cycled for 40 min at 85% of their measured ventilatory threshold (VT). During the transition from rest to exercise, hydrogen ion concentration ([H+]) increased significantly and bicarbonate concentration ([HCO3-]) decreased significantly in both groups. Total weak acid ([Atot]) increased significantly with exercise in both groups, whereas the strong ion difference ([SID]) and CO2 tension (PaCO2) did not change significantly with exercise. Values for [H+], [HCO3-], PaCO2, [Atot] and [SID] were significantly lower in the PG vs. CG under all experimental conditions. Acid-base responses to prolonged moderate exercise are quantitatively similar in the pregnant vs. non-pregnant state. However, pregnant women maintain a lower plasma [H+] (approximately 3 neq/L (1 neq/L=1 nmol/L)) throughout rest, exercise, and recovery, as a result of lower values for PaCO2 and [Atot], which is partly offset by a lower [SID]. The results indicate that prolonged moderate exercise appears to be well tolerated by healthy recreationally and occupationally active pregnant women.

Acid-Base Equilibrium↗
PubMed2005

Serial respiratory adaptations and an alternate hypothesis of respiratory control in human pregnancy.

This study determined the time course of changes in resting and exercising respiratory responses during the first half of human pregnancy, and examined the potential roles of plasma osmolality and the strong ion difference ([SID]) as mediators of pregnancy-induced increases in ventilation. Healthy active women (n = 11) were studied serially from 7 to 22 weeks gestation. Responses were compared with preconception data from 14 subjects (six of whom were tested in early pregnancy), and with late-gestation resting data from 10 additional women. Resting and exercising measurements included ventilation, PaCO2, progesterone, osmolality and [SID]. Results were analyzed using mixed-model linear regression. By 7 weeks gestation, increased ventilation resulted in a very large decrease in PaCO2 at rest and during moderate-intensity exercise. Large correlations (r > 0.5) between resting progesterone and PaCO2 support the traditional theory that circulating progesterone stimulates ventilation during pregnancy. The similar time course of changes and large correlations between raw and delta values of PaCO2 and each of plasma osmolality and [SID] also suggest that both variables may influence respiratory control at rest and during exercise in the first half of pregnancy. Future experiments should continue to explore the hypothesis that osmolality and [SID] contribute to pregnancy-induced respiratory changes.

Acclimatization↗
PubMed2005

Effects of human pregnancy on the ventilatory chemoreflex response to carbon dioxide.

This study examined the effects of human pregnancy on the central chemoreflex control of breathing. Subjects were two groups (n=11) of pregnant subjects (PG, gestational age, 36.5+/-0.4 wk) and nonpregnant control subjects (CG), equated for mean age, body height, prepregnant body mass, parity, and aerobic fitness. All subjects performed a hyperoxic CO2 rebreathing procedure, which includes prior hyperventilation and maintenance of iso-oxia. Resting blood gases and plasma progesterone and estradiol concentrations were measured. During rebreathing trials, end-tidal Pco2 increased, whereas end-tidal Po2 was maintained at a constant hyperoxic level. The point at which ventilation (Ve) began to rise as end-tidal Pco2 increased was identified as the central chemoreflex ventilatory recruitment threshold for CO2 (VRTco2). Ve levels below (basal Ve) and above (central chemoreflex sensitivity) the VRTco2 were determined. The VRTco2 was significantly lower in the PG vs. CG (40.5+/-0.8 vs. 45.8+/-1.6 Torr), and both basal Ve (14.8+/-1.1 vs. 9.3+/-1.6 l/min) and central chemoreflex sensitivity (5.07+/-0.74 vs. 3.16+/-0.29 l.min-1.Torr-1) were significantly higher in the PG vs. CG. Pooled data from the two groups showed significant correlations for resting arterial Pco2 with basal Ve, central chemoreflex sensitivity, and the VRTco2. The VRTco2 was also correlated with progesterone and estradiol concentrations. These data support the hypothesis that pregnancy decreases the threshold and increases the sensitivity of the central chemoreflex response to CO2. These changes may be due to the effects of gestational hormones on chemoreflex and/or nonchemoreflex drives to breathe.

Adult↗
PubMed2005

Maternal hemodynamics after oxytocin bolus compared with infusion in the third stage of labor: a randomized controlled trial.

OBJECTIVE: To assess the effects of oxytocin bolus or infusion on maternal hemodynamics in the third stage of labor. METHODS: In a randomized, double-blind, double-dummy fashion, 99 women received an intravenous oxytocin bolus (10 IU push) and 102 women received an infusion (10 IU in 500 mL saline at 125 mL/h) at delivery of the anterior shoulder. Mean arterial pressure and heart rate were measured every minute for 10 minutes, then every 5 minutes for the next 20 minutes. These serial measurements were analyzed using a 2-factor analysis of variance for repeated measures. RESULTS: Serial mean arterial pressure measures varied significantly between groups (interaction effect, P = .002). Mean arterial pressure (+/- standard deviation) nadirs were reached after 10 minutes, 80.9 (+/- 11.0) mm Hg in the bolus group compared with 77.0 (+/- 12.1) mm Hg in the dilute infusion group. The mean difference (95% confidence interval) between groups was 4.0 (0.7-7.2) mm Hg. Serial heart rate measures also varied between groups (interaction effect, P < .001). Mean heart rate (+/- standard deviation) peaked 1 minute after the oxytocin infusion, 115 (+/- 27) beats per minute (bpm) in the bolus group compared with 109 (+/- 21) bpm in the dilute infusion group. The mean difference (95% confidence interval) between groups was 6.6 bpm (-0.1 to 13.3). The dilute oxytocin infusion group experienced a greater mean estimated blood loss (423.7 mL compared with 358.1 mL, P = .029, t test), increased use of additional oxytocics (35.3% compared with 22.2%, P = .044, Fisher exact test) and a greater drop in hemoglobin (admission minus postpartum) (17.4g/L compared with 11.4g/L, P = .002, t test) compared with the oxytocin bolus group. CONCLUSION: Bolus oxytocin of 10 IU is not associated with adverse hemodynamic responses and can safely be administered to women with intravenous access in the third stage of labor for postpartum hemorrhage prophylaxis. LEVEL OF EVIDENCE: I.

Adult↗
PubMed2005

Effects of pregnancy on maternal work tolerance.

This review summarizes current information on the tolerance of healthy pregnant women and their fetuses to acute strenuous exertion. Maximal aerobic power, expressed in L x min(-1), is not significantly affected in women who maintain an active lifestyle, whereas values expressed in ml x kg(-1) x min(-1) decline with advancing gestational age in relation to maternal/fetal weight gain. Efficiency during standard exercise testing and the ventilatory anaerobic threshold (Tvent) also appear to be unaffected by pregnancy, but the ability to utilize carbohydrate and exercise anaerobically during brief strenuous exercise may be reduced. Fetal responses to short strenuous exercise are usually moderate and revert to baseline values within approximately 30 min postexercise. Future studies should examine alveolar gas exchange kinetics at the start of exercise and during recovery from both moderate and strenuous exertion. Existing studies of the responses of pregnant women to prolonged exercise have focused primarily on substrate utilization and glucose homeostasis. Other maternal responses to prolonged exercise that should be examined include acid-base regulation, temperature regulation, fluid and electrolyte balance, and perception of effort. Fetal reactions should also be examined in relation to maternal responses. Until evidence-based, occupation-specific guidelines become available, it is recommended that pregnant women use the Joint SOGC/CSEP Clinical Practice Guideline: Exercise in Pregnancy and the Postpartum Period, published by the Society of Obstetricians and Gynaecologists of Canada and the Canadian Society for Exercise Physiology (2003).

Adaptation, Physiological↗
PubMed2004

Chemoreflex control of breathing during wakefulness in healthy men and women.

This study used a modified CO(2) rebreathing procedure to examine the effect of gender on the chemoreflex control of breathing during wakefulness in healthy men (n = 14) and women (n = 14). Women were tested in the follicular phase of the menstrual cycle. During rebreathing trials, subjects hyperventilated to reduce the partial pressure of end-tidal CO(2) (Pet(CO(2))) below 25 Torr and were then switched to a rebreathing bag containing a normocapnic hypoxic or hyperoxic gas mixture. During the trial, Pet(CO(2)) increased, while O(2) was maintained at a constant level. The point at which ventilation began to rise as Pet(CO(2)) increased was identified as the ventilatory recruitment threshold (VRT). Ventilation below the VRT was measured, and the slope of the ventilatory response above the VRT was determined. Gender had no effect on the hyperoxic or hypoxic VRT for CO(2). Central chemoreflex sensitivity was significantly greater in men than women but not after correction for forced vital capacity. Measures of peripheral chemoreflex sensitivity were similar between genders. However, the slope of the tidal volume (Vt) response to hyperoxic and hypoxic CO(2) rebreathing (corrected and uncorrected) was greater in men than women, respectively. We conclude that central chemoreflex sensitivity is greater in men compared with women as reflected by differences in ventilatory (uncorrected) and Vt (corrected and uncorrected) responses to CO(2). However, gender has no significant effect on the central chemoreflex VRT for CO(2). The peripheral chemoreflex control of breathing during wakefulness is similar between men and women.

Adult↗
PubMed2004

Isolated gastroschisis in successive siblings: a case report and review of the literature.

BACKGROUND: Although gastroschisis occurring in siblings is rare, a number of cases have been reported. A variety of inheritance patterns and embryologic explanations have previously been suggested. Young maternal age appears to be a consistent risk factor. CASE: At age 17 years, Melanie (pseudonym) presented at 36 weeks' gestation and delivered a boy affected by gastroschisis. This condition had not been noted at a 13-week prenatal ultrasound. At age 18 years, Melanie delivered a second son with gastroschisis. There was no history of gastroschisis or other congenital anomaly in either parent's family. Melanie denied the use of alcohol, cigarettes, street drugs, and medications. She has since delivered 2 healthy children. CONCLUSION: There is a need for preconception counselling for women who have experienced a pregnancy complicated by gastroschisis, to discuss the low but possible risk of recurrence. Early ultrasound may allow for detection or reassurance.

Adolescent↗
PubMed2004

The role of regular physical activity in preeclampsia prevention.

Preeclampsia affects 2-7% of pregnancies and is a leading cause of maternal and fetal morbidity and mortality. Despite extensive study, the etiology of preeclampsia is poorly understood. Abnormal placental development, predisposing maternal constitutional factors, oxidative stress, immune maladaptation, and genetic susceptibility have all been hypothesized to contribute to the development of preeclampsia. Physical conditioning and preeclampsia have opposite effects on critical physiological functions. This suggests that regular prenatal exercise may prevent or oppose the progression of the disease. Epidemiologic studies show that occupational and leisure-time physical activity is associated with a reduced incidence of preeclampsia. We hypothesize that this protective effect results from one of more of the following mechanisms: 1) stimulation of placental growth and vascularity, 2) reduction of oxidative stress, and 3) exercise-induced reversal of maternal endothelial dysfunction. Future research should include prospective epidemiological case-control studies that accurately measure occupational and leisure-time physical activity. Controlled randomized clinical trials examining the effects of prenatal exercise on biochemical markers for endothelial dysfunction, placental dysfunction, and oxidative stress are also needed. If future research supports the idea that exercise effectively protects against preeclampsia, this would provide a low-cost intervention that could dramatically improve prenatal care for women at risk of this disease.

Epidemiologic Studies↗
PubMed2003

Effects of human pregnancy on fluid regulation responses to short-term exercise.

This study tested the hypothesis that human pregnancy alters fluid and electrolyte regulation responses to acute short-term exercise. Responses of 22 healthy pregnant women (PG; gestational age, 37.0 +/- 0.2 wk) and 17 nonpregnant controls (CG) were compared at rest and during cycling at 70 and 110% of the ventilatory threshold (VT). At rest, ANG II concentration was significantly (P < 0.05) higher in PG vs. CG, whereas plasma osmolality and concentrations of AVP, sodium, and potassium were significantly lower. Atrial natriuretic peptide concentration at rest was similar between groups. ANG II and AVP concentrations increased significantly from rest to 110% VT in CG only, whereas increases in atrial natriuretic peptide concentration were similar between groups. Increases in osmolality, and total protein and albumin concentrations from rest to both work rates were similar between the two groups. PG and CG exhibited similar shifts in fluid during acute short-term exercise, but the increases in ANG II and AVP were absent and attenuated, respectively, during pregnancy. This was attributed to the significantly augmented fluid volume state already present at rest in late gestation.

Adult↗
PubMed2003

Exercise in pregnancy and the postpartum period.

OBJECTIVE: To design Canadian guidelines advising obstetric care providers of the maternal, fetal, and neonatal implications of aerobic and strength-conditioning exercises in pregnancy. OUTCOMES: Knowledge of the impact of exercise on maternal, fetal, and neonatal morbidity, and of the maternal measures of fitness. EVIDENCE: MEDLINE search from 1966 to 2002 for English-language articles related to studies of maternal aerobic and strength conditioning in a previously sedentary population, maternal aerobic and strength conditioning in a previously active population, impact of aerobic and strength conditioning on early and late pregnancy outcomes, and impact of aerobic and strength conditioning on neonatal outcomes, as well as for review articles and meta-analyses related to exercise in pregnancy. VALUES: The evidence collected was reviewed by the Society of Obstetricians and Gynaecologists of Canada (SOGC Clinical Practice Obstetrics Committee) with representation from the Canadian Society for Exercise Physiology, and quantified using the evaluation of evidence guidelines developed by the Canadian Task Force on the Periodic Health Exam. RECOMMENDATIONS: 1. All women without contraindications should be encouraged to participate in aerobic and strength-conditioning exercises as part of a healthy lifestyle during their pregnancy. (II-1,2B) 2. Reasonable goals of aerobic conditioning in pregnancy should be to maintain a good fitness level throughout pregnancy without trying to reach peak fitness or train for an athletic competition. (II-1,2C) 3. Women should choose activities that will minimize the risk of loss of balance and fetal trauma. (III-C) 4. Women should be advised that adverse pregnancy or neonatal outcomes are not increased for exercising women. (II-1,2B) 5. Initiation of pelvic floor exercises in the immediate postpartum period may reduce the risk of future urinary incontinence. (II-1C) 6. Women should be advised that moderate exercise during lactation does not affect the quantity or composition of breast milk or impact infant growth. (I-A) VALIDATION: This guideline has been approved by the SOGC Clinical Practice Obstetrics Committee, the Executive and Council of SOGC, and the Board of Directors of the Canadian Society for Exercise Physiology. SPONSORS: This guideline has been jointly sponsored by the Society of Obstetricians and Gynaecologists of Canada and the Canadian Society for Exercise Physiology.

Adult↗
PubMed2003

Joint SOGC/CSEP clinical practice guideline: exercise in pregnancy and the postpartum period.

OBJECTIVE: To design Canadian guidelines advising obstetric care providers of the maternal, fetal, and neonatal implications of aerobic and strength-conditioning exercises in pregnancy. OUTCOMES: Knowledge of the impact of exercise on maternal, fetal, and neonatal morbidity, and of the maternal measures of fitness. EVIDENCE: MEDLINE search from 1966 to 2002 for English-language articles related to studies of maternal aerobic and strength conditioning in a previously sedentary population, maternal aerobic and strength conditioning in a previously active population, impact of aerobic and strength conditioning on early and late pregnancy outcomes, impact of aerobic and strength conditioning on neonatal outcomes, as well as for review articles and meta-analyses related to exercise in pregnancy. VALUES: The evidence collected was reviewed by the Society of Obstetricians and Gynaecologists of Canada (SOGC Clinical Practice Obstetrics Committee) with representation from the Canadian Society for Exercise Physiology, and quantified using the evaluation of evidence guidelines developed by the Canadian Task Force on the Periodic Health Exam.

Exercise↗