Phrenic Nerve Conduction Abnormalities Correlate with Diaphragmatic Descent in Chronic Obstructive Pulmonary Disease

Figures & data

Table 1.  Flow volume loop parameters and PaO2 level in the studied COPD patients

	Mean ± SD (range)
FVC:
actual (L)	2.4 ± 1 (1.07–4.8)
% of predicted	57 ± 21.2 (23.5–102.4)
FEV1:
actual (L)	1.3 ± 0.7 (0.5–3.2)
% of predicted	44.4 ± 22.2 (15.1–96.7)
FEV1/FVC	52.6 ± 12.1 (29.9–68.8)
FEF 25-75:
actual (L/s)	1.2 ± 0.9 (0.4–3.1)
% of predicted	41 ± 26.8 (15.9–99.1)
PEFR:
actual (L/s)	3.6 ± 1.8 (1.3–7.9)
% of predicted	45.7 ± 21.1 (16.5–92.5)
FET (s)	5.9 ± 1.8 (3.2–9.7)
PaO2 (mm Hg)	71.5 ± 12.4 (47–89)

FVC forced vital capacity.

FEV₁ forced expiratory flow rate in the first second.

FEF 25–75 forced expiratory flow during the middle portion of forced expiration.

PEFR peak expiratory flow rate.

FET forced expiratory time.

PaO2 partial pressure of oxygen in arterial blood.

Table 2.  Radiographic measures of lung hyperinflation in COPD patients and controls

	Patients (n = 40) mean ± SD (range)	Controls (n = 27) mean ± SD (range)	t-test	P value
Lung height (cm):
Right lung	25.4 ± 2.1 (21.5–30)	22 ± 1.1 (20–23.4)	6.301	<0.001*
Left lung	26 ± 2.1 (22.5–30.5)	23.5 ± 1.3 (20.6–24.7)	3.456	<0.003*
Lung width (cm)	28.2 ± 2.1 (23–33)	27.9 ± 1 (26.6–29.4)	0.107	0.916
Cardiac size (cm)	12.3 ± 1.5 (9–15)	12.5 ± 1.1 (11.1–14.6)	0.402	0.675
Diaphragmatic level:
Right side	10.3 ± 0.7 (9–11.5)	9.5 ± 0.4 (9–10)	4.095	0.001*
Left side	10.5 ± 0.5 (9.5–11.5)	9.7 ± 0.3 (9.5–10)	4.223	<0.001*
RSAS width (cm)	3.7 ± 0.7 (2.5–5.4)	2.1 ± 0.2 (1.8–2.4)	9.244	<0.001*
DAOD on PA film (º):
Right side	11.9 ± 2.7 (7–17)	20.1 ± 2.1 (17–24)	8.479	<0.001*
Left side	14.2 ± 2.5 (9.5–20)	24.8 ± 2.1 (21–28)	11.566	<0.001*
DAOD on lateral film (º):
Right side	9 ± 2 (6–12.5)	20 ± 1.7 (17–23)	13.644	<0.001*
Left side	9.2 ± 2.1 (6–13)	20.1 ± 1.8 (18–23)	12.927	<0.001*

*P is significant if ≤0.05.

RSAS retrosternal air space.

DAOD diaphragmatic angle of depression.

PA postero-anterior.

Table 3.  Phrenic nerve conduction studies in COPD patients and controls

	Patients (n = 40)
	Right side	Left side	Controls (n = 27)
	mean ± SD (range)	mean ± SD (range)	mean ± SD (range)	ANOVA	P^1	P^2	P^3
Xiphoid process recording:
Latency (ms)	8 ± 1 (5.8–10.8)	7.9 ± 1 (5.9–10.7)	7.8 ± 0.6 (6.3–8.6)	0.626	0.671	0.342	0.560
Amplitude (mV)	1.4 ± 0.6 (0.2–3.1)	1.5 ± 0.7 (0.1–3.6)	1.2 ± 0.4 (0.7–2.1)	0.425	0.549	0.388	0.197
7^th intercostal space recording:
Latency (ms)	9.4 ± 2.8 (6.1–22.3)	9.6 ± 3.1 (6.4–20.7)	7.7 ± 0.6 (6.4–8.7)	0.03*	0.805	0.021*	0.012*
Amplitude (mV)	0.7 ± 0.4 (0.1–1.9)	0.7 ± 0.4 (0.1–1.9)	1.3 ± 0.5 (0.6–2)	<0.001*	0.760	<0.001*	<0.001*

*P is significant if ± 0.05.

P¹, the comparison of right and left sides of patients with COPD.

P², the comparison of right side of patients with COPD and controls.

P³, the comparison of left side of patients with COPD and controls.

Table 4.  Side-to-side latency difference (ms) of the recorded phrenic nerve potentials in COPD patients and controls

	Patients (n = 40)	Controls (n = 27)
	mean ± SD (range)	mean ± SD (range)	t-test	P
Xiphoid process recording	0.49 ± 0.57 (0–2.6)	0.3 ± 0.24 (0–0.8)	1.718	0.094
7^th intercostal space recording	1.96 ± 2.75 (0–11.6)	0.5 ± 0.32 (0–0.9)	3.266	0.002*

*P is significant if ±0.05.

Figure 1. Diaphragmatic compound muscle action potentials recorded in a patient with COPD (a) showing prolongation of the distal latency of the potentials recorded over the xyphoid process on the right side and the 7^th intercostal space on both sides with normal amplitude. Diaphragmatic potentials recorded in a healthy subject are also shown (b).

Table 5.  Correlation analyses between electrophysiological parameters, dyspnea score, flow volume loop parameters, PaO2, and radiographic measures of lung hyper-inflation

	Xiphoid process recording				7^th intercostal space recording
	Latency		Amplitude		Latency		Amplitude
	Right side	Left side	Right side	Left side	Right side	Left side	Right side	Left side
Clinical parameters:
MRC dyspnea score	0.91	0.67	0.21	0.75	0.62	0.97	0.27	0.58
Flow volume loop parameters:
FVC:
actual	0.8	0.88	0.09	0.08	0.33	0.56	0.77	0.5
% of predicted	0.44	0.87	0.08	0.07	0.26	0.4	0.79	0.3
FEV1:
actual	0.64	0.74	0.08	0.16	0.18	0.51	0.84	0.26
% of predicted	0.43	0.56	0.07	0.13	0.12	0.32	0.93	0.19
FEV1/FVC	0.59	0.42	0.08	0.21	0.14	0.13	0.97	0.22
FEF 25–72:
actual	0.44	0.38	0.26	0.54	0.18	0.75	0.8	0.21
% of predicted	0.43	0.36	0.29	0.57	0.16	0.67	0.79	0.17
PEFR:
actual	0.43	0.69	0.1	0.16	0.19	0.27	0.86	0.62
% of predicted	0.23	0.48	0.1	0.21	0.15	0.20	0.84	0.48
FET	0.63	0.59	0.81	0.47	0.41	0.19	0.70	0.94
PaO2	0.89	0.85	0.11	0.72	0.88	0.16	0.83	0.83
Severity of airflow limitation	0.92	0.84	0.06	0.19	0.28	0.57	0.5	0.44
Radiographic measures of lung hyperinflation:
Lung height:
Right lung	0.01*		0.35		0.93		0.62
Left lung		0.03*		0.34		0.43		0.2
Lung width	0.18	0.37	0.05	0.12	0.54	0.59	0.47	0.46
Cardiac size	0.21	0.09	±0.01*	±0.02*	0.12	0.36	0.20	0.37
Diaphragmatic level:
Right side	0.52		0.08		0.23		0.62
Left side		0.56		0.08		0.48		0.29
RSAS	0.13	0.39	0.27	0.21	0.58	0.35	0.76	0.99
DAOD on PA film:
Right lung	0.9		0.94		0.22		0.9
Left lung		0.51		0.88		0.66		0.21
DAOD on lateral films:
Right lung	±0.01*		0.78		±0.04*		0.9
Left lung		–0.02*		0.94		±0.01*		0.46

*P is significant if ±0.05.

FVC forced vital capacity.

FEV₁ forced expiratory flow rate in the first second.

FEF 25–75 forced expiratory flow during the middle portion of forced expiration.

PEFR peak expiratory flow rate.

FET forced expiratory time.

PaO2 partial pressure of oxygen in arterial blood.

RSAS retrosternal air space.

DAOD diaphragmatic angle of depression.

PA postero-anterior.