Pubertal development in ICSI children

BACKGROUND

To date, information on the pubertal development of adolescents born after ICSI is scarce, since the very first cohort is only now reaching young adulthood. In this study, pubertal development at the age of 14 was characterized in a longitudinally followed cohort of ICSI-conceived teenagers and compared with that of a spontaneously conceived (SC) control group.

METHODS

Pubertal development was assessed by Tanner staging (breast, genital and pubic hair development) and age at menarche in 217 singleton ICSI-conceived children (116 boys, 101 girls) and 223 SC peers (115 boys, 108 girls). ICSI teenagers were part of a previously published cohort followed since birth; controls were a cross-sectional sample recruited from schools. Differences in pubertal development between ICSI and SC children were analyzed with logistic regression of current status data.

RESULTS

Mean age at menarche was similar in ICSI and SC girls (13.1 ± 1.2 versus 13.1 ± 1.4 years; P = 0.8). Breast developmental at the age of 14 years was less advanced in ICSI females compared with SC females, even after adjustment for demographic (age, BMI), genetic (maternal age at menarche), social (maternal educational level) and early life factors (birthweight, gestational age and maternal parity) [odds ratio (OR) 0.5; 95% confidence interval (CI) 0.3-0.8]. After adjustment, genital development in the 14-year-old boys was comparable in the ICSI and SC groups (OR 1.1; 95% CI 0.7-1.8), pubic hair development was comparable in the ICSI and SC groups, for both males (OR 0.9; 95% CI 0.7-1.6) and females (OR 0.7; 95% CI 0.4-1.3).

CONCLUSIONS

We found that pubertal development, characterized by menarche, genital development in males and pubic hair development in males and females, was comparable in the ICSI and SC groups. Breast developmental was less advanced in ICSI females compared with SC peers, even after adjustment for known potential confounders. In order to confirm that progression through subsequent stages of pubertal development occurs on a timely basis in ICSI teenagers, long-term follow-up studies up to adulthood are required.

Oral contraceptive use and cancer. Findings in a large cohort study, 1968-2004

We examined cancer incidence in relation to oral contraceptive (OC) use in the Oxford Family Planning Association contraceptive study. The study includes 17032 women, recruited at family planning clinics at ages 25-39 years between 1968 and 1974, who were using OCs, a diaphragm, or an intrauterine device. Follow-up data were available until 2004. OC use was not significantly related to nonreproductive cancer. Breast cancer findings (844 cases) likewise were very reassuring (rate ratio (RR) comparing women ever using OCs with those never doing so 1.0, 95% confidence interval (CI) 0.8-1.1). There was a strong positive relationship between cervical cancer incidence (59 cases) and duration of OC use (RR comparing users for 97+ months with nonusers 6.1, 95%CI, 2.5-17.9). Uterine body cancer (77 cases) and ovarian cancer (106 cases) showed strong negative associations with duration of OC use: RRs for 97+ months of use were 0.1 (95%CI, 0.0-0.4) and 0.3 (95%CI, 0.1-0.5) respectively. This apparent protective effect for both cancers persisted more than 20 years after stopping OCs. Combining data for cancers of the cervix, uterine body and ovary, the age adjusted RR for women ever using OCs compared with those never doing so was 0.7 (95%CI, 0.5-0.8). Beneficial effects of OCs on the gynaecological cancers thus outweighed adverse effects.

Return of fertility in nulliparous women after discontinuation of the intrauterine device: comparison with women discontinuing other methods of contraception

OBJECTIVE

To clarify the effect of the using the intrauterine device on fertility in nulliparous women.

DESIGN

Prospective cohort study of two groups of nulliparous women, one recruited while using an intrauterine device and the other while using an oral contraceptive.

SETTING

Seventeen family planning clinics in England and Scotland.

SAMPLE

1,071 nulliparous, married women, aged 18-40 years, 558 of whom contributed information to the main objective of the study.

METHODS

The women were recruited between 1982 and 1985 and followed up annually to 1994. Dates and reasons for any contraceptive method changes (which were most frequently to barrier methods) were recorded, together with the outcome of any pregnancies, at each follow up.

MAIN OUTCOME MEASURES

The number of nulliparous women giving birth at term after stopping contraception (oral contraceptive, intrauterine device or barrier method) in order to conceive.

RESULTS

Women who stopped using a barrier method to achieve a planned pregnancy conceived most quickly: 54% were delivered after one year vs 39% of intrauterine device and 32% of oral contraceptive users (log rank P = 0.002). There was no association between fertility and duration of oral contraceptive use: However, short term intrauterine device users (< 42 months) showed a fertility pattern more favourable than seen in those discontinuing oral contraceptives, with increasing duration of intrauterine device use being associated with decreasing fertility (linear trend P = 0.005); the fertility of women who had used the intrauterine device for 78 + months was the most impaired (28% were delivered by 12 months vs 46% of short term users; at 36 months the corresponding figures were 79% vs 91%). This association remained after adjusting for potential confounding factors, including maternal age, husband's social class, and history of gynaecological illnesses, factors which themselves had independent associations with fertility.

CONCLUSIONS

Long term intrauterine device use in nulliparous women appears to be associated with an increased risk of fertility impairment.

Oral contraception and ear disease: findings in a large cohort study

A number of authors have suggested that oral contraceptives may increase the risk of certain ear diseases, especially otosclerosis and vestibular disorders, although the amount of published information on this topic is limited. We have analyzed the available data on ear disease in the Oxford-Family Planning Association contraceptive study that includes 17,032 women followed for periods of up to 26 years. No evidence of any adverse effect of oral contraceptives on ear disease was detected. A protective effect of oral contraceptives against wax in the ear has been described in the Royal College of General Practitioners oral contraception study. The amount of data available in the Oxford-Family Planning Association study was too small to permit confirmation or refutation of this finding.

Skin disorders in relation to oral contraception and other factors, including age, social class, smoking and body mass index. Findings in a large cohort study

BACKGROUND

Over the years, a substantial number of scientific papers has been published considering the possible relationship between oral contraceptive use and various skin disorders.

OBJECTIVES

We aimed to investigate the possible effects of oral contraceptives and other factors including age, social class, smoking and body mass index on the occurrence of hospital referral for skin disorders within the Oxford Family Planning Association (Oxford-FPA) contraceptive study.

METHODS

We carried out a cohort study with long-term follow up of 17,032 women aged 25-39 years recruited at 17 family planning centres in England and Scotland between 1968 and 1974. The main outcome measure was the pattern of referral to hospital for skin disorders among the participants. The conditions considered (number of women affected in parentheses) were: malignant melanoma (48); other skin cancers (83); benign skin neoplasms (384); boils and cellulitis (334); eczema and dermatitis (327); erythematous disease (54); psoriasis (92); hypertrophic and atrophic conditions (59); diseases of the nails (80); diseases of the hair and hair follicles (74); diseases of the sebaceous glands (362); pigmented naevi (383); and unspecified eruptions (199). Some of these disease categories are broad, which complicates interpretation of the findings.

RESULTS

As the data relate to hospital referrals, while most skin disorders are largely managed within primary care, it is difficult to know to what extent our findings can be generalized to disease patterns in the community. None the less, a number of interesting results emerged. These included increased risks (approximately twofold) of referral to hospital for boils and cellulitis in heavy women, for psoriasis in women who smoke, and for pigmented naevi in women of higher social class. Referral for pigmented naevi was reduced by about half in women with a high body mass index. Of the oral contraceptive associations studied, we consider that only an increased risk of referral for eczema or dermatitis in current or recent pill users (relative risk 1.6, 95% confidence interval 1.2-2.1) might reflect a causal relationship. There was no increased risk in past users nor was the risk related to duration of use. These findings are very similar to those reported from the Royal College of General Practitioners oral contraception study.

CONCLUSIONS

Hospital referral for certain skin disorders was related to age, social class, smoking and body mass index within the Oxford-FPA study. Hospital referral for skin disorders generally seems to be unrelated to oral contraceptive use within the study, the possible exception being eczema and dermatitis, which occur more commonly in current and recent pill users than in non-users.

Oral contraception and other factors in relation to back disorders in women: findings in a large cohort study

The Oxford-Family Planning Association contraceptive study includes 17,032 women, initially aged 25-39 years, recruited at 17 British family planning centers during the interval 1968-1974 and subsequently followed-up for periods up to 26 years. This article examines the pattern of referral to hospital for back disorders among these women. Certain back disorders have been reported to occur more frequently in oral contraceptive users than in other women, and back pain has also been reported in some women consequent to using an intrauterine device. The disorders considered were spinal osteoarthritis, displaced cervical disc, displaced lumbar disc, other and unspecified displaced disc, cervicalgia, unspecified back pain, and sprains and strains of the back. Spinal osteoarthritis and unspecified backache were the only two conditions significantly related (both positively) to age. Displaced lumbar disc and other and unspecified displaced disc were strongly positively related to height and weight. Unspecified backache showed similar, but less striking (in terms of the magnitude of the relative risks), associations with height and weight. Little evidence was found of any association between oral contraceptive use and any of the back disorders, and the same was true for intrauterine device use.

Risk of myocardial infarction, angina and stroke in users of oral contraceptives: an updated analysis of a cohort study

OBJECTIVES

To investigate risk of myocardial infarction, angina and stroke in users of contraceptive pills compared with users of other methods of contraception.

DESIGN

Prospective cohort study, with recruitment between 1968 and 1974 and annual follow up until the age of 45 years. After this age, only women who had never used oral contraception or those who had used it for eight or more years continued to be followed up annually until July 1994.

SETTING

Seventeen family planning clinics in England and Scotland.

POPULATION

17,032 women aged between 25 and 39 years at entry to the study.

MAIN OUTCOME MEASURES

Occurrence of angina, myocardial infarction or stroke that was associated with either hospital admission or outpatient referral to hospital or death.

RESULTS

Increased risk of myocardial infarction in oral contraceptive users was observed only in women who were heavy smokers at entry to the study. In this subgroup the relative risk of a myocardial infarction was 4.2 (95% CI 1.4-16.6) in ever users of oral contraception compared with non-users, 4.9 (1.2-23.6) in current users, and 4.0 (1.3-16.2) in ex-users. In all current users the relative risk of angina was 0.5 (0.1-1.4), and the relative risk of ischaemic stroke was 2.9 (1.3-6.7). The increased risk of ischaemic stroke did not persist in ex-users.

CONCLUSIONS

Use of oral contraception is associated with increased risk of ischaemic stroke and increased risk of myocardial infarction (only in heavy smokers), but no increased risk of angina. These increased risks need to be considered within the context of the very low absolute risks of cardiovascular disease in this population. 5880 women need to take oral contraception for one year to cause one extra stroke, and 1060 women who are heavy smokers need to take it for one year to cause one extra myocardial infarction.

Oral contraception and eye disease: findings in two large cohort studies

AIM—To investigate the relation between oral contraceptive use and certain eye diseases.
METHODS—Abstraction of the relevant data from the two large British cohort studies of the effects of oral contraception, the Royal College of General Practitioners' (RCGP) Oral Contraception Study and the Oxford-Family Planning Association (Oxford-FPA) Contraceptive Study. Both cohort studies commenced in 1968 and were organised on a national basis. Between them they have accumulated over 850 000 person years of observation involving 63 000 women.
RESULTS—The conditions considered in the analysis were conjunctivitis, keratitis, iritis, lacrimal disease, strabismus, cataract, glaucoma, retinal detachment, and retinal vascular lesions. With the exception of retinal vascular lesions, there was no consistent evidence of important increases in risk of eye diseases in users of oral contraception. There was about a twofold increase in the risk of retinal vascular lesions in recent pill users in both studies (statistically significant only in the RCGP study). The increase was not limited to any specific type of lesion and may well reflect diagnostic bias.
CONCLUSION—Oral contraceptive use does not appear to increase the risk of eye disease, with the possible exception of retinal vascular lesions.

 Keywords: oral contraception; eye disease; cohort studies

Oral contraception and other factors in relation to hospital referral for fracture. Findings in a large cohort study

There is good evidence that estrogens and progestogens have an important effect on bone metabolism. This article explores the relationship between oral contraceptive (OC) use and fractures occurring at various sites among the 17,032 participants in the Oxford-Family Planning Association contraceptive study, which now includes information accumulated during 310,000 woman-years of observation between 1968 and 1994. In total, 1308 women suffered at least one fracture during the follow-up period, which was largely confined to premenopausal years. When all fractures were combined, there was a modest, but highly significant trend (p < 0.001) of increasing risk with total duration of oral contraceptive use. In addition, there was statistically significant heterogeneity (p < 0.01) when overall fracture rates were examined in relation to recency of oral contraceptive use during the premenopausal lifespan. The highest relative risk (1.3, 95% CI 1.1-1.5) was for current or recent oral contraceptive users; however, viewed as a whole, no clear pattern of risk was apparent. Examination of the data for individual fracture sites (including the lower end of the radius/ulna) did not provide any evidence of a protective effect of oral contraceptive use. These results are closely similar to those reported from the Royal College of General Practitioners Oral Contraception Study in 1993.

Epidemiology of genital prolapse: observations from the Oxford Family Planning Association Study

OBJECTIVE

To explore the epidemiology of uterovaginal and post-hysterectomy prolapse.

DESIGN

Cohort study.

SETTING

Seventeen large family planning clinics in England and Scotland.

POPULATION

17,032 women who attended family planning clinics between 1968 and 1974, aged between 25 and 39 years at study entry.

METHODS

Annual follow up by interview, postal or telephone questionnaire until July 1994. Further details on all hospital admissions were obtained from the hospital discharge summaries. All women were flagged at time of recruitment in the NHS central registers.

MAIN OUTCOME MEASURE

In-patient admission with diagnosis of prolapse (ICD codes 8th Revision 623.0-623-9).

RESULTS

The incidence of hospital admission with prolapse is 2.04 per 1000 person-years of risk. Age, parity, calendar period and weight were significantly associated with risk of an inpatient admission with prolapse after adjustment for principal confounding factors. Significant trends were observed with regard to smoking status and obesity (Quetelet Index) at entry to the study and risk of prolapse. Social class, oral contraceptive use and height were not significantly associated with risk of prolapse. The incidence of prolapse which required surgical correction following hysterectomy was 3.6 per 1000 person-years of risk. The cumulative risk rises from 1% three years after a hysterectomy to 5% 15 years after hysterectomy. The risk of prolapse following hysterectomy is 5.5 times higher (95% CI 3.1-9.7) in women whose initial hysterectomy was for genital prolapse as opposed to other reasons.

CONCLUSION

Among the potential risk factors that were investigated, parity shows much the strongest relation to prolapse.

Combined oral contraceptives and liver disease

Although some information is available about the risk of liver tumors associated with combined oral contraceptive use, little is known about the relationship with other hepatic problems. Data from two large long-term observational studies, the Royal College of General Practitioners (RCGP) Oral Contraception Study and the Oxford-Family Planning Association (Oxford-FPA) Study, were used to examine this issue. Observations accumulated over a period of up to 27 years were available for each study. The incidence of liver disease in each study was low. There was no evidence of an increased risk of serious liver disease overall among current or former pill users. The RCGP study found a modest increased risk of mild liver disease associated with oral contraceptive use which declined after four years of use and after cessation of use. This increased risk occurred in women who had used oral contraceptives containing more than 50 micrograms of estrogen.

Oral contraceptives and cervical cancer--further findings from the Oxford Family Planning Association contraceptive study

In 1983, we reported results from the Oxford Family Planning Association contraceptive study regarding the association between oral contraceptives (OCs) and cervical neoplasia, after a 10 year follow-up of a cohort of 17,000 women. Further findings from this study are reported here after an additional 12 years of follow-up. A nested case--control design was used in which cases were all women diagnosed under 45 years of age with invasive carcinoma (n = 33), carcinoma in situ (n = 121) or dysplasia (n = 159). Controls were randomly selected from among cohort members and matched to cases on exact year of birth and clinic attended at recruitment to study. Conditional logistic regression analysis was used to determine odds ratios (ORs) and 95% confidence intervals (CIs) associated with various aspects of OC use relative to never users adjusted for social class, smoking, age at first birth and ever use of diaphragm or condom. Ever users of OCs had a slightly elevated OR for all types of cervical neoplasia combined (OR = 1.40, 95% CI 1.00-1.96). Odds ratios were highest for invasive carcinoma (OR = 4.44, 95% CI 1.04-31.6), intermediate for carcinoma in situ (OR = 1.73, 95% CI 1.00-3.00) and lowest for dysplasia (OR = 1.07, 95% CI 0.69-1.66). The elevated risk associated with OC use appeared to be largely confined to current or recent (last use in the past 2 years) long-term users of OCs. Among current or recent users, ORs for all types of cervical neoplasia combined were 3.34 (95% CI 1.96-5.67) for 49-72 months of use, 1.69 (95% CI 0.97-2.95) for 73-96 months and 2.04 (95% CI 1.34-3.11) for 97 or more months. These results suggest a possible effect of OC use on later stages of cervical carcinogenesis, although residual confounding due to sexual factors or human papillomavirus (HPV) infection cannot be ruled out.

Endometrial and ovarian cancer and oral contraceptives--findings in a large cohort study

Many case-control studies have shown that oral contraceptives protect against endometrial cancer and epithelial ovarian cancer, but little information is available from cohort studies. The findings from the Oxford Family Planning Association contraceptive study are reported here; the relative risks for ever users of oral contraceptives in comparison with never users were 0.1 (95% confidence interval 0.0-0.7) for endometrial cancer and 0.4 (95% confidence interval 0.2-0.8) for ovarian cancer. There was a strong negative relationship between duration of oral contraceptive use and ovarian cancer risk. Thus, in comparison with never users of oral contraceptives, the relative risk for users of up to 48 months' duration was 1.0 (95% confidence interval 0.4-2.5), while the relative risk for users of 97 months' duration or more was only 0.3 (95% confidence interval 0.1-0.7).

Oral contraceptive use and benign gallbladder disease; revisited

An analysis is described of 482 women with benign gallbladder disease (surgically confirmed in 407) identified in the Oxford Family Planning Association contraceptive study. There was no significant overall association between oral contraceptive use and gallbladder disease (relative risk ever use to never use 1.1, 95% confidence interval 0.9 to 1.3). Likewise, duration of oral contraceptive use had no significant effect (relative risk 97 or more months use to never use 1.1, 95% confidence interval 0.8 to 1.5). There was no indication of any interaction between oral contraceptive use and body mass index or oral contraceptive use and age in the production of disease. It is concluded that it is unlikely that oral contraceptives are of either clinical or public health significance in relation to the occurrence of gallbladder disease.

A mathematical model of the human ventilatory response to isocapnic hypoxia

A mathematical model of the ventilatory response to a period of sustained isocapnic hypoxia in humans has been developed. After a step into hypoxia, there is an initial rapid increase in ventilation (on-transient) followed by a slow decline. At the relief of hypoxia, there is a rapid decrease in ventilation (off-transient); the magnitude of this off-transient is smaller than that of the on-transient. Previously, the asymmetry between the on- and off-transients has been dealt with by modeling the steps into and out of hypoxia separately. The current objective was to model the whole of the response by allowing the peripheral sensitivity to hypoxia to decline during the sustained exposure to hypoxia. The model was fitted to breath-by-breath data from 20-min periods of hypoxia (end-tidal oxygen 50 Torr) at two different levels of end-tidal carbon dioxide tension from five subjects. The model was able to describe the features of the ventilatory changes well, including the slow decline and the asymmetry.

Epidemiology of endometriosis in women attending family planning clinics

OBJECTIVE

To describe the epidemiology of endometriosis in women attending family planning clinics with special reference to contraceptive methods.

DESIGN

Non-randomised cohort study with follow up of subjects for up to 23 years. Disease was measured by first hospital admission rates since endometriosis can be diagnosed with accuracy only at laparotomy or laparoscopy.

SETTING

17 family planning centres in England and Scotland.

SUBJECTS

17,032 married white women aged 25-39 years at entry during 1968-74 who were taking oral contraceptives or using an intrauterine device or diaphragm. About 99% of the women approached agreed to participate and annual loss to follow up was about 0.3%.

MAIN OUTCOME MEASURES

Diagnosis of endometriosis, age, parity, and history of contraceptive use.

RESULTS

Endometriosis was significantly related to age, peaking at ages 40-44 (chi 2 for heterogeneity = 30.9, p < 0.001). Endometriosis was not linked to duration of taking oral contraceptives. Nevertheless, the risk of endometriosis was low in women currently taking oral contraceptives (relative risk 0.4; 95% confidence interval 0.2 to 0.7), but higher in women who had formerly taken them (1.8; 1.0 to 3.1 in women who had stopped 25-48 months previously) compared with women who had never taken the pill. A similar pattern was seen for use of intrauterine devices (relative risk 0.4 (0.2 to 0.7) in current users and 1.4 (0.4 to 3.2) in users 49-72 months previously compared with never users). No association was found between endometriosis and use of the diaphragm.

CONCLUSIONS

Oral contraceptives seem to temporarily suppress endometriosis. Endometriosis may be diagnosed late in women using intrauterine devices as pain and bleeding occur with both.

Oral contraceptives and pregnancy in relation to peptic ulcer

There is evidence in the scientific literature that peptic ulceration occurs less frequently during pregnancy than at other times. This encouraged us to examine the pattern of hospitalisation for peptic ulcer in the Oxford-Family Planning Association contraceptive study. In total, 175 women in the study had been hospitalised for peptic ulcer; 105 had duodenal disease, 55 had gastric disease and 22 had disease of unspecified site (some had disease at more than one location). Hospitalisation for peptic ulcer increased with age, parity and cigarette smoking. In addition, hospitalisation was at a low rate during pregnancy and was not seen at all during the 12 months following delivery. There was no relationship between hospitalisation for peptic ulcer and total duration of oral contraceptive use. Likewise, there was no significant relationship with recency of oral contraceptive use, but the lowest rate of hospitalisation was in current users of the pill.

An assessment of central-peripheral ventilatory chemoreflex interaction in humans

The independence of the central and peripheral chemoreflexes has been tested in humans. Acute metabolic acidosis generated by a prior bout of brief, hard exercise was used to stimulate primarily the peripheral chemoreceptors, and respiratory acidosis generated by inhaled CO2 was used to stimulate both central and peripheral chemoreceptors. Seven healthy young men were studied. Ventilation and arterial pH, PCO2 and PO2 were recorded. Peripheral chemoreflex sensitivity to hypoxia during acute metabolic acidosis was repeatedly determined by measuring ventilation in euoxia (PETO2 = 100 Torr) and hypoxia (PETO2 = 50 Torr) as the subject recovered from exercise-induced acidosis. Peripheral chemoreflex sensitivity to hypoxia during CO2 inhalation was repeatedly determined by measuring ventilation in euoxia and hypoxia at two levels of hypercapnia (PETCO2 = 45 Torr and PETCO2 = 50 Torr). The ventilatory sensitivity to hypoxia at matched arterial pH values was not significantly different between conditions of high (CO2 inhalation) and low (metabolic acidosis) central chemoreceptor activity. We therefore conclude that interaction between central and peripheral chemoreflexes was non-significant in all subjects.

Analyses of human respiratory flow patterns

Respiratory drives follow various afferent pathways to the respiratory centres; nevertheless, steady-state breathing patterns described in terms of tidal volumes and phase durations are largely independent of the nature of the respiratory stimulus. Flow has now been recorded during steady states from six subjects in rest and hyperpnoea induced by exercise, and hypercapnia in euoxia and in hypoxia (asphyxia). Flow patterns from different stimuli were compared isopnoeically. Quantitative methods allowed the patterns to be described in terms of several variables. The consistent small differences in isopnoeic flow patterns were: In asphyxia, the initial inspiratory acceleration was greater than in hypercapnia, and the peak flow was reached earlier. In exercise the peak flow occurred later in inspiration, and the expiratory flow was maintained high until nearer the end of the phase than with the chemical drives so that the flow pattern was less angular in shape. Stimulus-dependent effects, obvious during transient changes, are greatly attenuated rather than absent in steady states.

Ehlers-Danlos syndrome type IV: diagnosis and therapy of associated bowel perforation

Ehlers-Danlos syndrome type IV is a heritable disease of type III collagen metabolism. This diagnosis is suspected in a patient with a combination of clinical manifestations and family history, but it is confirmed only by culture of the patient's skin fibroblasts and demonstration of a defect in type III collagen metabolism. The disease may rarely present with spontaneous colonic perforation, a complication traditionally treated by primary closure of the perforated segment and creation of an end colostomy. Attempts at bowel reanastomosis have often resulted in repeated colon perforations. We present the first patient with Ehlers-Danlos type IV syndrome to develop a colon perforation proximal to an end colostomy, and discuss the surgical strategy to prevent recurrences of this and other postoperative complications associated with the syndrome.

Changes in peripheral chemoreflex sensitivity during sustained, isocapnic hypoxia

One hypothesis concerning the origin of hypoxic ventilatory decline is that hypoxia acts centrally to depress peripheral chemoreflex loop activity. To investigate possible changes in peripheral chemoreflex loop activity during sustained, isocapnic hypoxia, the ventilatory responses to four one minute pulses of either extra hypoxia (45 Torr) or carbon dioxide (8 Torr above resting levels) were measured in man at minutes 2, 7, 12, and 17 of a 23 min isocapnic, hypoxic period (50 Torr). For hypoxia, the first pulse response (130%) was significantly greater (P less than 0.05) than the fourth response (74%). For CO2, pulse responses 2 and 3 (101 and 103%, respectively) were significantly greater (P less than 0.05) than the fourth response (91%). A central depression of peripheral chemoreflex loop activity should affect peripheral sensitivities to CO2 and hypoxia equally. Our results suggest that the peripheral sensitivity to hypoxia declined more than that to CO2, implying a peripheral chemoreceptor origin for hypoxic ventilatory decline.

Changes in arterial K+ and ventilation during exercise in normal subjects and subjects with McArdle's syndrome

1. We have examined the relationship between ventilation (VE), lactate (La) and arterial plasma K+ concentrations [( K+]a) during incremental exercise in six normal subjects and in four subjects with McArdle's syndrome (myophosphorylase deficiency) who do not become acidotic during exercise. 2. In normal subjects, [K+]a rose to ca 7 mM at the point of exhaustion. The time courses of the increases in VE, La and [K+]a were all similar during the exercise period. La reached its peak concentration during the recovery from exercise when both VE and [K+]a were returning to resting levels. 3. McArdle's subjects, like normal subjects, had a non-linear ventilatory response during incremental exercise. Their [K+]a was closely related to VE throughout exercise and recovery. 4. The arterial pH of McArdle's subjects, rather than remaining constant, actually rose from the onset of exercise. 5. For a given level of exercise, the levels of VE and [K+]a were greater in the McArdle's subjects than in normal subjects. 6. These findings are consistent with the idea that hyperkalaemia may contribute significantly to the drive to breathe, especially during heavy exercise.