1440
Negative-pressure ventilation for chronic obstructive pulmonary disease The history of research into ventilatory support is littered with uncontrolled trials. In this issue (p 1425) a large study from workers at McGill University in Montreal compares domiciliary active and sham negative-pressure ventilation in severe chronic obstructive pulmonary disease (COPD). Basing their study on the hypothesis that respiratory muscle fatigue plays a prominent part in the development of ventilatory failure in advanced COPD, Shapiro and colleagues delivered intermittent negative-pressure ventilation (NPV) by means of a body-suit, with the aim of resting the inspiratory muscles. Sham assisted ventilation was applied surprisingly successfully with the same apparatus, with external pressure limited to about - 5 cm H2O compared with - 30 cm HO in patients randomised to active treatment. Most patients were normocapnic and arterial blood gas tensions were not monitored during NPV. Patients tolerated the intervention poorly and nearly all were unable to sleep in the body-suit. Results of the active and sham limbs of the trial were similar, with no significant improvement in measures of breathlessness and exercise tolerance and no effect on arterial blood gas tensions, respiratory muscle strength, or quality of life. What should we conclude from this study? There are several possible interpretations: (a) NPV is of no value in end-stage COPD; (b) treatment failed because the inspiratory muscles were not sufficiently rested owing to inadequacy of the ventilatory technique and its application; (c) the primary goal of muscle rest is of little importance compared with other aims such as control of deranged nocturnal and diurnal arterial blood gas tensions and improvement in cardiac function. With respect to NPV being of no value at all, two small controlled trials of this technique in COPD1,2 have likewise shown no overall benefit. These results differ from earlier uncontrolled data3,4 which suggested an improvement in arterial blood gas tensions and ventilatory muscle strength with NPV, especially in hypercapnic COPD patients. Studies of domiciliary NPV in hypercapnic restrictive ventilatory disease have shown sustained improvement in arterial blood gas tensions and quality of life,although nearly all these patients used NPV
during sleep. In the McGill study, the patients used NPV during the day because they found that it disrupted sleep and the equipment was difficult to assemble without assistance. Sleep fragmentation during NPV is usually due to a combination of upper airway obstruction6,7 and chest-wall discomfort. Poor compliance and a detrimental effect on the quality of life would seem to be the likely consequences of asking patients to remain immobile using ventilatory equipment for 5 h a day.
As Shapiro et al point out, the amount of reduction in respiratory muscle activity to produce "rest" is unknown. Their aim of a 50% reduction in diaphragm surface electromyogram for 35 h a week was achieved in less than a third (29%) of patients. One interpretation of this result is that, since NPV was ineffectually applied, no judgment can be reached regarding its efficacy in COPD. The main aim of respiratory muscle rest can also be challenged. The belief that respiratory muscle fatigue
the development of ventilatory and that inspiratory muscle rest will insufficiency this reverse process is attractive and widely held, but proof of this hypothesis is scanty. A study8 of the contractile properties of the diaphragm in COPD patients with chronic hyperinflation showed that the COPD patients had more efficient inspiratory muscles than control subjects; this feature undermines the rationale for the McGill study. Levine and co-workers9 have confirmed that NPV has no significant clinical effect on ventilatory muscle endurance in severe COPD. Ventilatory support by use of nasal intermittent positive-pressure ventilation (NIPPV) seems more promising than NPV since this technique is better tolerated and does not provoke upper airway obstruction. Preliminary studies of nasal mask ventilation in COPD have produced conflicting results;10,11 this discrepancy probably reflects differences in patient selection and the type of ventilator used. Data from one uncontrolled trial," in which NIPPV was used specifically to control nocturnal hypoventilation in hypercapnic patients, indicate that domiciliary nocturnal nasal ventilation is feasible in COPD. Improvements were noted in nocturnal and diurnal arterial blood gas tensions and in sleep quality. The mechanism of action seems to be via an increase in the ventilatory response to hypercapnia and a reduction in ventilatory load. Again, there was no effect on inspiratory muscle function. Before we dismiss ventilatory support in end-stage COPD, improvement of the technique by means of nasal ventilation and a shift in approach to controlling arterial blood gas tensions should be considered. The effects on sleep, ventilatory drive, and cardiac function need to be assessed. The McGill study leads the way in showing that controlled studies are not only possible but also mandatory in evaluating new applications of technology. The next step is a controlled comparison of the cost-effectiveness of nocturnal nasal ventilation with standard long-term oxygen therapy in hypercapnic patients with COPD. contributes
to
1. Zibrak JD, Hill NS, Federman EC, Kwa SL, O’Donnell C. Evaluation of
intermittent long term negative pressure ventilation in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1988; 138: 1515-18. 2. Celli B, Lee H, Criner G, et al. Controlled trial of external negative pressure ventilation in patients with severe chronic airflow obstruction. Am Rev Respir Dis 1989; 140: 1251-56. 3. Braun NMT, Marino WS. Effect of daily intermittent rest of the respiratory muscles in patients with severe chronic airflow limitation (CAL). Chest 1984; 85 (suppl): 59-60.
1441
4.
Cropp A, Dimarco AF. Effects of intermittent negative pressure ventilation on respiratory muscle function in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1987; 135: 1056-61.
5. Sawicka EH, Loh L, Branthwaite MA. Domiciliary ventilatory support: an analysis of outcome. Thorax 1988; 43: 31-35. 6. Levy RD, Bradley TD, Newman SL, et al. Negative pressure ventilation: effects of ventilation during sleep in normal subjects. Chest 1989; 95: 95-99. 7. Goldstein RS, Molotiu N, Skrastins R, et al. Reversal of sleep induced hypoventilation and chronic respiratory failure by nocturnal negative pressure ventilation in patients with restrictive ventilatory impairment. Am Rev Respir Dis 1987; 135: 1049-55. 8. Similowski T, Sheng Y, Gauthier AP, et al. Contractile properties of the human diaphragm during chronic hyperinflation. N Engl J Med 1991; 325: 917-23. 9. Levine S, Levy SF, Henson DJ. Effect of negative pressure ventilation on ventilatory muscle endurance in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1992; 146: 722-29. 10. Strumpf DA, Millman RP, Carlisle CC, et al. Nocturnal positive pressure ventilation via nasal mask in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1991; 144: 1234-39. 11. Elliott MW, Mulvey DA, Moxham J, et al. Domiciliary ventilation in COPD: mechanisms underlying changes in arterial blood gas tensions. Eur Respir J 1991; 4: 1044-52.
Mapping sexual lifestyles The molecular structure of HIV has proved more amenable to study than have patterns of human sexual behaviour, but an understanding of such behaviour is central to the prevention of AIDS and to predictions about the course of the epidemic.! How often, in what ways, and with whom do people have sex? Answering these questions has perplexed many social scientists. Will people lie about their sex histories? Even asking the questions alarms some policy makers. Publication last week of two major studies of sexual lifestyles in France and Britain is an important step forward.2,3 There are no surprises in the sense of discovering some uncharted territory of human behaviour: within any one society, human sexual behaviour is highly heterogeneous. Many people have a few sexual partners and a few have a great many. The importance of these reports is that a picture composed of travellers’ tales has been replaced by a map drawn on scientific principles. Most couples are monogamous: 73% of men and 79% of women reported that they had only 1 partner in the past year, while nearly 5 % of men and just under 1 % of women reported 10 or more partners in the past 5 years. The highest rate of partner change is in unmarried urban men and women, under age 25, who began intercourse before age 16. The patterns in Britain and France are similar: 77% of men and 78% of women in France had 1 partner in the past year (although the French lived up to their sexual stereotype in that about a third of the men and half of the women aged 35-49 reported having 2 or more partners at the same time). Over the decades, the map of sexual lifestyles has changed. Younger cohorts report starting sex at an earlier age and having more partners. In France the number of men whose sexual initiation was with a prostitute has fallen from 10% for those now aged 45-69 to 2 % for men aged 20-24. More specific changes are also occurring as a result of knowledge about AIDS. The groups with most partners are those
most
likely to seek an HIV test and (at least in France)
to use condoms: 75% of homosexual men, 65% of heterosexual men, and 50% of heterosexual women reporting multiple partners used condoms. The lifetime number of sexual partners for the UK is 9-9 for men and 3-4 for women (11-0 and 3-3 for France). The variance for men was 6575 compared with 165 for women, which indicates a much larger spread in the number of partners of men. Perhaps the most important limitation of the random sample survey technique used is that it is unlikely to have captured a significant number of prostitutes, who account for part of the difference in the mean number of male and female sexual partners. 6% of men report at least 1 homosexual experience (11-9% in London) and 0-8% of men and 0-4% of women report intravenous drug use (equivalent to 100 000 drug users in the UK). The incidence of AIDS in the UK in 1991 was 23-5 per million inhabitants and 1 in 12 cases was the result of heterosexual transmission.Mutually monogamous couples with no risk of sexually transmitted HIV are remarkably rare. Many people run a low but finite risk of transmission; a few people, who can identify themselves, run a considerable risk. Consequently, everyone needs to be educated about AIDS and to have access to condoms, while intensive education and services can best be focused on the more vulnerable groupS.5 The study suggests that more attention should be given to the use of sexually transmitted disease (STD) clinics for education about AIDS (1 in 7 men with 5 or more female partners has attended an STD clinic in the past 5 years). HIV is a fragile virus that is difficult to transmit; the key to understanding the epidemic may be that relatively small changes in the variables affecting acquisition and transmission have a powerful effect on the spread of the epidemic.6Heterosexual spread in the west has been less rapid than some commentators feared but spread in developing countries has been more rapid. Studies from Africa show a swifter partner change than in Europe; the use of prostitutes, for example, is greater in Thailand; and condom availability and the treatment of STDs is not as good in developing countries. Some or all of these factors may be relevant. The heterogeneity of sexual behaviour necessitates large and therefore expensive studies-the British study involved 18 876 interviews of people age 16-59 and cost 1000 000 ($1 500 000). Sexual behaviour is also a very private matter; careful pilot surveys were done and 184 consistency checks were included in the final survey.One way of ensuring confidentiality was by never linking the results with a name at any point in the study. The response rates were 65-75% in the two countries. Data from Britain will be published in book form in 1993. The old maps of sexual lifestyles were filled with fabulous monsters. The British study had a stormy beginning and Margaret Thatcher blocked
Negative-pressure ventilation for chronic obstructive pulmonary disease The history of research into ventilatory support is littered with uncontrolled trials. In this issue (p 1425) a large study from workers at McGill University in Montreal compares domiciliary active and sham negative-pressure ventilation in severe chronic obstructive pulmonary disease (COPD). Basing their study on the hypothesis that respiratory muscle fatigue plays a prominent part in the development of ventilatory failure in advanced COPD, Shapiro and colleagues delivered intermittent negative-pressure ventilation (NPV) by means of a body-suit, with the aim of resting the inspiratory muscles. Sham assisted ventilation was applied surprisingly successfully with the same apparatus, with external pressure limited to about - 5 cm H2O compared with - 30 cm HO in patients randomised to active treatment. Most patients were normocapnic and arterial blood gas tensions were not monitored during NPV. Patients tolerated the intervention poorly and nearly all were unable to sleep in the body-suit. Results of the active and sham limbs of the trial were similar, with no significant improvement in measures of breathlessness and exercise tolerance and no effect on arterial blood gas tensions, respiratory muscle strength, or quality of life. What should we conclude from this study? There are several possible interpretations: (a) NPV is of no value in end-stage COPD; (b) treatment failed because the inspiratory muscles were not sufficiently rested owing to inadequacy of the ventilatory technique and its application; (c) the primary goal of muscle rest is of little importance compared with other aims such as control of deranged nocturnal and diurnal arterial blood gas tensions and improvement in cardiac function. With respect to NPV being of no value at all, two small controlled trials of this technique in COPD1,2 have likewise shown no overall benefit. These results differ from earlier uncontrolled data3,4 which suggested an improvement in arterial blood gas tensions and ventilatory muscle strength with NPV, especially in hypercapnic COPD patients. Studies of domiciliary NPV in hypercapnic restrictive ventilatory disease have shown sustained improvement in arterial blood gas tensions and quality of life,although nearly all these patients used NPV
during sleep. In the McGill study, the patients used NPV during the day because they found that it disrupted sleep and the equipment was difficult to assemble without assistance. Sleep fragmentation during NPV is usually due to a combination of upper airway obstruction6,7 and chest-wall discomfort. Poor compliance and a detrimental effect on the quality of life would seem to be the likely consequences of asking patients to remain immobile using ventilatory equipment for 5 h a day.
As Shapiro et al point out, the amount of reduction in respiratory muscle activity to produce "rest" is unknown. Their aim of a 50% reduction in diaphragm surface electromyogram for 35 h a week was achieved in less than a third (29%) of patients. One interpretation of this result is that, since NPV was ineffectually applied, no judgment can be reached regarding its efficacy in COPD. The main aim of respiratory muscle rest can also be challenged. The belief that respiratory muscle fatigue
the development of ventilatory and that inspiratory muscle rest will insufficiency this reverse process is attractive and widely held, but proof of this hypothesis is scanty. A study8 of the contractile properties of the diaphragm in COPD patients with chronic hyperinflation showed that the COPD patients had more efficient inspiratory muscles than control subjects; this feature undermines the rationale for the McGill study. Levine and co-workers9 have confirmed that NPV has no significant clinical effect on ventilatory muscle endurance in severe COPD. Ventilatory support by use of nasal intermittent positive-pressure ventilation (NIPPV) seems more promising than NPV since this technique is better tolerated and does not provoke upper airway obstruction. Preliminary studies of nasal mask ventilation in COPD have produced conflicting results;10,11 this discrepancy probably reflects differences in patient selection and the type of ventilator used. Data from one uncontrolled trial," in which NIPPV was used specifically to control nocturnal hypoventilation in hypercapnic patients, indicate that domiciliary nocturnal nasal ventilation is feasible in COPD. Improvements were noted in nocturnal and diurnal arterial blood gas tensions and in sleep quality. The mechanism of action seems to be via an increase in the ventilatory response to hypercapnia and a reduction in ventilatory load. Again, there was no effect on inspiratory muscle function. Before we dismiss ventilatory support in end-stage COPD, improvement of the technique by means of nasal ventilation and a shift in approach to controlling arterial blood gas tensions should be considered. The effects on sleep, ventilatory drive, and cardiac function need to be assessed. The McGill study leads the way in showing that controlled studies are not only possible but also mandatory in evaluating new applications of technology. The next step is a controlled comparison of the cost-effectiveness of nocturnal nasal ventilation with standard long-term oxygen therapy in hypercapnic patients with COPD. contributes
to
1. Zibrak JD, Hill NS, Federman EC, Kwa SL, O’Donnell C. Evaluation of
intermittent long term negative pressure ventilation in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1988; 138: 1515-18. 2. Celli B, Lee H, Criner G, et al. Controlled trial of external negative pressure ventilation in patients with severe chronic airflow obstruction. Am Rev Respir Dis 1989; 140: 1251-56. 3. Braun NMT, Marino WS. Effect of daily intermittent rest of the respiratory muscles in patients with severe chronic airflow limitation (CAL). Chest 1984; 85 (suppl): 59-60.
1441
4.
Cropp A, Dimarco AF. Effects of intermittent negative pressure ventilation on respiratory muscle function in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1987; 135: 1056-61.
5. Sawicka EH, Loh L, Branthwaite MA. Domiciliary ventilatory support: an analysis of outcome. Thorax 1988; 43: 31-35. 6. Levy RD, Bradley TD, Newman SL, et al. Negative pressure ventilation: effects of ventilation during sleep in normal subjects. Chest 1989; 95: 95-99. 7. Goldstein RS, Molotiu N, Skrastins R, et al. Reversal of sleep induced hypoventilation and chronic respiratory failure by nocturnal negative pressure ventilation in patients with restrictive ventilatory impairment. Am Rev Respir Dis 1987; 135: 1049-55. 8. Similowski T, Sheng Y, Gauthier AP, et al. Contractile properties of the human diaphragm during chronic hyperinflation. N Engl J Med 1991; 325: 917-23. 9. Levine S, Levy SF, Henson DJ. Effect of negative pressure ventilation on ventilatory muscle endurance in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1992; 146: 722-29. 10. Strumpf DA, Millman RP, Carlisle CC, et al. Nocturnal positive pressure ventilation via nasal mask in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1991; 144: 1234-39. 11. Elliott MW, Mulvey DA, Moxham J, et al. Domiciliary ventilation in COPD: mechanisms underlying changes in arterial blood gas tensions. Eur Respir J 1991; 4: 1044-52.
Mapping sexual lifestyles The molecular structure of HIV has proved more amenable to study than have patterns of human sexual behaviour, but an understanding of such behaviour is central to the prevention of AIDS and to predictions about the course of the epidemic.! How often, in what ways, and with whom do people have sex? Answering these questions has perplexed many social scientists. Will people lie about their sex histories? Even asking the questions alarms some policy makers. Publication last week of two major studies of sexual lifestyles in France and Britain is an important step forward.2,3 There are no surprises in the sense of discovering some uncharted territory of human behaviour: within any one society, human sexual behaviour is highly heterogeneous. Many people have a few sexual partners and a few have a great many. The importance of these reports is that a picture composed of travellers’ tales has been replaced by a map drawn on scientific principles. Most couples are monogamous: 73% of men and 79% of women reported that they had only 1 partner in the past year, while nearly 5 % of men and just under 1 % of women reported 10 or more partners in the past 5 years. The highest rate of partner change is in unmarried urban men and women, under age 25, who began intercourse before age 16. The patterns in Britain and France are similar: 77% of men and 78% of women in France had 1 partner in the past year (although the French lived up to their sexual stereotype in that about a third of the men and half of the women aged 35-49 reported having 2 or more partners at the same time). Over the decades, the map of sexual lifestyles has changed. Younger cohorts report starting sex at an earlier age and having more partners. In France the number of men whose sexual initiation was with a prostitute has fallen from 10% for those now aged 45-69 to 2 % for men aged 20-24. More specific changes are also occurring as a result of knowledge about AIDS. The groups with most partners are those
most
likely to seek an HIV test and (at least in France)
to use condoms: 75% of homosexual men, 65% of heterosexual men, and 50% of heterosexual women reporting multiple partners used condoms. The lifetime number of sexual partners for the UK is 9-9 for men and 3-4 for women (11-0 and 3-3 for France). The variance for men was 6575 compared with 165 for women, which indicates a much larger spread in the number of partners of men. Perhaps the most important limitation of the random sample survey technique used is that it is unlikely to have captured a significant number of prostitutes, who account for part of the difference in the mean number of male and female sexual partners. 6% of men report at least 1 homosexual experience (11-9% in London) and 0-8% of men and 0-4% of women report intravenous drug use (equivalent to 100 000 drug users in the UK). The incidence of AIDS in the UK in 1991 was 23-5 per million inhabitants and 1 in 12 cases was the result of heterosexual transmission.Mutually monogamous couples with no risk of sexually transmitted HIV are remarkably rare. Many people run a low but finite risk of transmission; a few people, who can identify themselves, run a considerable risk. Consequently, everyone needs to be educated about AIDS and to have access to condoms, while intensive education and services can best be focused on the more vulnerable groupS.5 The study suggests that more attention should be given to the use of sexually transmitted disease (STD) clinics for education about AIDS (1 in 7 men with 5 or more female partners has attended an STD clinic in the past 5 years). HIV is a fragile virus that is difficult to transmit; the key to understanding the epidemic may be that relatively small changes in the variables affecting acquisition and transmission have a powerful effect on the spread of the epidemic.6Heterosexual spread in the west has been less rapid than some commentators feared but spread in developing countries has been more rapid. Studies from Africa show a swifter partner change than in Europe; the use of prostitutes, for example, is greater in Thailand; and condom availability and the treatment of STDs is not as good in developing countries. Some or all of these factors may be relevant. The heterogeneity of sexual behaviour necessitates large and therefore expensive studies-the British study involved 18 876 interviews of people age 16-59 and cost 1000 000 ($1 500 000). Sexual behaviour is also a very private matter; careful pilot surveys were done and 184 consistency checks were included in the final survey.One way of ensuring confidentiality was by never linking the results with a name at any point in the study. The response rates were 65-75% in the two countries. Data from Britain will be published in book form in 1993. The old maps of sexual lifestyles were filled with fabulous monsters. The British study had a stormy beginning and Margaret Thatcher blocked
