Effects of Chronic Obstructive Pulmonary Disease and Obstructive Sleep Apnea on Cognitive Functions: Evidence for a Common Nature

Table 1

Studies examining the effects of COPD on cognitive functions.

Study	Sample characteristics	Type of study	Results
Crews et al. 2001 [9]	47 patients, (FEV1) < 25%; age = 55.45 ± 6.67	Case control—normative study	50% of the patients exhibited impaired memory performance. Clinically notable frequencies of impairment (greater than 20%) were found on language abilities, executive functions, and psychomotor speed.
Antonelli-Incalzi et al. 2007 [28]	149 patients, FEV1 = 36.6 ± 17.8%, age = 69.3 ± 8.5	Clinical case—normative study	Patients exhibited a general cognitive decline.
Hung et al. 2009 [29]	4150 patients, 29% severe (oxygen depended or disease related activity limited), age = 62.6 ± 1.8; 71% nonsevere, age = 62.9 ± 1.8	Community sampled case—control study	Only severe COPD was associated with lower cognitive performance
Etnier and Berry 2001 [30]	98 patients, age = 58–80,; FEV1 = 58.34 ± 16.41%	Exercise intervention follow-up study	Age, aerobic fitness, or pulmonary function are predictive of cognitive performance on fluid intelligence, reaction time, and working memory span.
Borak et al. 1996 [31]	90 patients (severe COPD treated with long-term oxygen therapy)	Clinical case study	Patients presented poor visual, verbal, and spatial memory.
Kozora et al. 2002 [32]	30 patients, age = 66.5, FEV1 = 39.9 ± 1.6%	Clinical case—control study	Significant impairment in visual attention, verbal memory, constructional abilities, psychomotor speed, and executive functions.
Kozora and Make 2000 [33]	30 patients (severe COPD, followed 3 weeks of rehabilitation), 29 untreated COPD patients, 21 healthy controls	Clinical case—control study	Significant group differences were found on sustained visual attention, visual memory, and language abilities.
Vos et al. 1995 [34]	39 patients, age = 65.9 ± 5,; FEV1 = 33 ± 10%, 38 healthy controls	Case—control study	Lower attention performance of COPD patients in comparison to healthy controls.
Klein et al. 2010 [35]	60 patients, age = 63.2 ± 9.8; FEV1 = 36.4 ± 12.5%, 60 healthy controls	Clinical case—control study	Significant group differences found in phasic alertness and orienting but not in executive attention. Reaction time was significantly slower in the COPD group. Differences were found in verbal, visual learning, and logical thinking.
Emery et al. 2001 [36]	29 patients, age = 67.8 ± 7.4, FEV1 = 43 ± 17%, 29 controls	Clinical study of exercise effects	Only the improved performance in verbal fluency test was associated with exercise.
Kozora et al. 2005 [37]	39 patients, age = 64.8 ± 4.9; FEV1% = 24.9 ± 11, 39 healthy controls	Clinical case—control study	Patients with moderate-to-severe emphysema had impaired attention, verbal memory, and constructional abilities.
Watanabe et al. 2001 [38]	1 patient, 71 yrs old, FEV1 = 39%	Clinical case study of lung volume reduction surgery	All cognitive functions improved after lung volume reduction surgery.
Orth et al. 2006 [39]	32 patients, age = 57,4 ± 8,2; FEV1 = 50,4 ± 18,2%, 10 healthy controls	Clinical case—control study	Patients demonstrated significantly worse results than healthy controls in intelligence, simple, selective, and sustained attention tasks.
Antonelli-Incalzi et al. 2003 [40]	15 patients (COPD with severe hypoxemia), 18 (COPD without hypoxemia), 10 healthy controls	Clinical case—control study	Patients performed below normal in verbal attainment, attention, and deductive thinking tasks.
Ortapamuk and Naldoken 2006 [41]	8 patients (COPD with hypoxemia and hypercapnia), age = 52.6 ± 5.4,; 10 patients (with stable COPD), age = 54.8 ± 6.9, FEV1 = 33.9 ± 13%,; 10 healthy controls	Clinical case—control study	Scores in verbal memory, delayed recall, and attention tasks were significantly lower in COPD patients than healthy controls. No differences in psychomotor speed.
Kozora et al. 1996 [42]	32 patients (COPD with mean partial arterial oxygen pressure 68.8 mm Hg, 73% receiving supplementary oxygen), age = 70.3, 31 healthy controls	Clinical case—control study	COPD patients performed significantly worse than controls in verbal fluency and attention tasks.
Incalzi et al. 1993 [43]	36 patients (severe COPD, receiving oxygen therapy), age = 69 ± 10,; 29 normal adults (69 ± 7 yr),; 20 normal elderly adults (78 ± 2 yr),; 26 patients (Alzheimer-type dementia, (72 ± 2 yr), 28 patients (multi-infarct dementia, 70 ± 8 yr)	Clinical case—control study	48.5% of patients with COPD had a specific pattern of cognitive deterioration characterized by impairment in verbal and verbal memory tasks, well-preserved visual attention, and diffuse worsening of the other functions.
Antonelli-Incalzi et al. 2006 [44]	149 patients, age = 68.7 ± 8.5, FEV1 = 36.5 ± 18.0%	Clinical case study	The prevalence of cognitive impairment was 32.8%. Visual memory was not impaired.
Borson et al. 2008 [45]	18 patients (mild to severe COPD),; 2 patients (FEV1 = 50–79%),; 8 patients (FEV1 = 30–49%),; 8 patients (FEV1 < 30%), age = 68.5 ± 8.0, 9 healthy controls	Clinical case—control study	Performance in verbal memory, land psychomotor speed was impaired.
Liesker et al. 2004 [46]	30 patients, FEV1 = 49 ± 8% age = 64.8,; 20 controls	Clinical case—control study	COPD patients performed significantly worse than controls in psychomotor speed tasks.
Stuss et al. 1997 [47]	18 patients; FEV1 = 74 ± 30%, age = 66.4 ± 7.6	Clinical case—control study	Intelligence scores and psychomotor speed and memory abilities were within average range.
Antonelli-Incalzi et al. 2009 [48]	54 patients (hypoxemic COPD),; age = 68.8 ± 9.0, FEV1 = 36.9 ± 16.5%	Clinical study	Patients had impaired performance; in copying drawings with landmarks
Incalzi 1997 [49]	42 patients (COPD with hypoxemia and hypercarbia), FEV1 = 34 ± 9%, age = 70 ± 9.7, 27 normal subjects,; 31 patients (Alzheimer's disease),; 26 older normal subjects	Clinical case—control study	The overall cognitive performance of COPD patients was significantly inferior to that of the rest of the groups. Both passive recognition and active recall of learned material were severely impaired in COPD patients.
Fioravanti et al. 1995 [50]	50 patients	Case study	30% of COPD patients had impaired immediate verbal memory.
Kozora et al. 1995 [51]	40 patients, age = 64,; 40 healthy controls	Clinical case—control study	COPD patients were significantly impaired during copying.
Kozora et al. 1998 [52]	59 patients, age = 66.7,; 31 healthy controls, age = 65.9	Clinical case—control study	COPD patients performed significantly worse than controls in two tasks (verbal fluency and digit span) but not at a clinically impaired range.