Subjects

The study population consisted of three normal subjects, four subjects with neuromuscular disorders with or without associated chest wall deformities (restrictive group), and five subjects with severe COPD (obstructive group). Subject characteristics are shown in table 1.

In the restrictive group, two subjects (nos. 5,7) were receiving nocturnal intermittent positive pressure ventilation and one (no. 6) was on intermittent positive pressure ventilation continuously, all through fenestrated tracheostomies. Subject no. 4 was in acute respiratory failure, but was not receiving mechanical ventilatory support. In the obstructive group, three subjects (nos. 8,10,12) were stable outpatients, and two (no. 9,11) were hospitalized in the intensive care unit with acute respiratory failure. They were not being mechanically ventilated.

The study protocol was approved by the Ethics Committee of the Montreal Chest Hospital Centre and informed consent was obtained from all subjects. canadian pharmacy viagra

Nasal Positive Pressure Ventilation

Intermittent positive pressure ventilation was applied through a comfortable, tightly fitted nasal mask (Respironics Inc, Monroeville, PA) designed for the provision of nasal continuous positive airway pressure. The mask was connected by rigid tubing to a pressure- cycled ventilator (Thompson Maxivent, Puritan-Bennett Corp, Boulder, CO) in control mode. The ratio of inspiratory time to total time per breath was 0.4. Supplemental oxygen (1-2 L/min) was provided for three oxygen-dependent subjects (no. 6,9,11) through a side port of the nasal mask to maintain oxygen saturation greater than 90 percent during spontaneous breathing. Oxygen flow re­mained constant for the remainder of the study.

Table 1—Clinical Characteristics of Study Population

Subject

Age

FEV,

FVC

Pa02*

PaC02*

No

Sex

(yrs)

Diagnosis

(% pred)

(% pred)

FEV/FVC

(mm Hg)


FI
o2

(mm Hg)

pH*

Normal

1

M

31

Normal

103

106

0.80

2

M

34

Normal

96

96

0.77

3

M

57

Normal

94

96

0.72

Mean

41

98

99

0.76

SEM

8.2

2.7

3.3

0.02

Restrictive

4

F

33

Kyphoscoliosis, myelomeningocele

13

15

0.83

63

.21

58

7.30

5

M

31

Syringomyelia

29

35

0.73

79

.21

49

7.35

6

F

72

Amyotrophic lateral sclerosis

41

33

0.83

78

.28

53

7.41

7

F

25

Kyphoscoliosis, myelomeningocele

47

48

0.84

82

.21

46

7.36

Mean

40

33

33

0.81

76

52

7.36

SEM

10.7

7.5

6.8

0.03

4.3

2.6

0.02

Obstructive

8

F

55

COPD

22

58

0.31

53

.21

49

7.38

9

M

62

COPD

38

88

0.24

58

.28

63

7.32

10

M

64

COPD

26

67

0.32

58

.21

46

7.40

11

M

54

COPD

13

37

0.30

71

.28

89

7.30

12

M

64

COPD

23

77

0.24

68

.21

45

7.40

Mean

60

24

65

0.28

62

58

7.36

SEM

2.2

4.0

8.7

0.02

3.4

8.3

0.02

Measurements

Mask pressure (Pmask) was measured by a differential pressure transducer (model MP-45, ± 100 cmHaO, Validyne Corp, North- ridge, С A) connected by rigid tubing to a side port of the mask. Rib cage and abdominal movements were monitored using respi­ratory inductive plethysmography (RIP) (Respitrace, AMI Inc, Ardsley, NY). Bands were placed at nipple and umbilical levels and calibration was performed with the isovolume technique. Oxyhe­moglobin saturation was obtained using a finger pulse oximeter (Biox 3700, Ohmeda, Boulder, CO) in the subjects from the restrictive and obstructive groups. Expired carbon dioxide gas tension was continuously measured using an infrared COz analyzer (Applied Electrochemistry Inc, Sunnyvale, CA) in four subjects (nos. 3,5,9,10) with a sampling catheter inserted into the mask and positioned in front of the nares. Arterial blood gas levels were evaluated in three subjects (nos. 4,5,11) during spontaneous breath­ing and NPPV. buy generic cialis