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D Henson

Publications and source records attributed to D Henson.

At least 19 recordsLinked to original sources
PubMed2000

Assessment of the diurnal variation in central corneal thickness and intraocular pressure for patients with suspected glaucoma.

OBJECTIVE: To assess whether a single daily measurement using ultrasonic pachymetry gives a representative assessment of mean central corneal thickness (CCT) in patients with suspected glaucoma and whether diurnal changes in CCT are related to diurnal variations in intraocular pressure (IOP). DESIGN: Cross-sectional study. METHOD: Central CCT and IOP were measured by a single observer in 56 eyes of 28 patients with suspected glaucoma using an ultrasonic pachymeter and a Goldmann tonometer. Four measurements were made over a 24-hour period: at 8:00 AM, 12:00 PM, 4:00 PM, and 8:00 PM. MAIN OUTCOME MEASURES: Intraocular pressure and pachymetry. RESULTS: Mean IOP was 19.80 mmHg at 8:00 AM (95% confidence interval [CI], 18.95-20.66 mmHg), 20.38 mmHg at 12:00 PM (95% CI, 19.49-21.26 mmHg), 19.91 mmHg at 4:00 PM (95% CI, 19.99-21.83 mmHg), and 19.23 mmHg at 8:00 PM (95% CI, 18.35-20.11 mmHg). Mean CCT was 569.4 microm (95% CI, 560.2-578.7 microm), 567.6 microm (95% CI, 558.4-576.7 microm), 569.1 microm (95% CI, 559.5-578.6 microm), and 567.2 microm (95% CI, 557.9-576.4 microm) at the four respective time points. There was no significant correlation between IOP and CCT in any patient (Pearson rank correlation coefficient); nor was there any significant correlation between the mean diurnal variations of IOP and CCT. CONCLUSIONS: In this group of patients with suspected glaucoma, there was no significant variation in CCT. Therefore, a single measurement of CCT is sufficient when assessing patients with suspected glaucoma. There was no correlation between change of IOP and change of CCT.

Aged↗
PubMed1999

Relationship between corneal thickness and measured intraocular pressure in a general ophthalmology clinic.

OBJECTIVE: To assess whether central corneal thickness (CCT) is a confounding factor in the classification of patients attending for glaucoma assessment in a district general hospital. DESIGN: Cross-sectional study by a single observer. PARTICIPANTS: Patients attending a general ophthalmic clinic: 235 clinically normal eyes, 52 eyes with normal-tension glaucoma (NTG), 335 eyes with primary open-angle glaucoma (POAG), 12 eyes with pseudoexfoliative glaucoma (PXE), 42 eyes with chronic angle closure glaucoma (CACG), and 232 glaucoma suspect (GS) eyes. INTERVENTION: Central corneal thickness was measured using ultrasonic pachymetry. MAIN OUTCOME MEASURE: Correlation of CCT and diagnosis. RESULTS: Mean CCT was 553.9 microm (95% confidence intervals [CI] for the mean, 549.0-558.8 microm) in the clinically normal eyes, 550.1 microm (95% CI, 546.6-553.7 microm) in the POAG eyes, 514.0 microm (95% CI, 504.8-523.3 microm) in the NTG eyes, 530.7 microm (95% CI, 511.2-550.1 microm) in the PXE eyes, 559.9 microm (95% CI, 546.8-573.0 microm) in the CACG eyes, and 579.5 microm (95% CI, 574.8-584.1 microm) in the GS eyes. The differences of mean CCT between the groups were highly significant (P< 0.001 analysis of variance). Eighty-five percent of eyes with NTG and only 36% of eyes with POAG had a mean CCT of 540 microm or less. Thirteen percent of eyes with POAG and 42% of GS eyes had a mean CCT greater than 585 microm. CONCLUSIONS: The CCT measurement is desirable in patients attending for glaucoma assessment in a district general hospital to avoid misclassification resulting from the relationship between CCT and tonometric pressure. Central corneal thickness alone is not an accurate predictor for the clinical diagnosis in this group of eyes. However, many eyes diagnosed as having NTG have thin corneas, which would tend to lower the tonometrically recorded intraocular pressure (IOP), so the finding of a less-than-normal thickness cornea introduces some doubt as to the diagnosis of NTG. For the GS eyes, most eyes had thick corneas, which would tend to increase the tonometrically recorded IOP. Thus, GS eyes with modest elevation of IOP and a thick cornea may be at low risk of progressing to POAG. Thus, many patients with "high IOPs" and a thick CCT do not necessarily have high IOPs and may not need to be followed as GS eyes.

Cornea↗
PubMed1996

The sensation of dyspnea during exercise is not determined by the work of breathing in patients with heart failure.

OBJECTIVES: The present study sought to investigate whether the work of breathing was reduced after heart transplantation. Accordingly, the tension time index of the diaphragm was measured in patients with heart failure and in transplant recipients. BACKGROUND: Patients with heart failure are frequently limited by exertional dyspnea that may be due to the increased work of breathing. After heart transplantation, exertional dyspnea is markedly diminished. Whether work of breathing is reduced in posttransplant recipients is unknown. METHODS: Nine patients with heart failure, six normal subjects and six heart transplant recipients were studied. Transdiaphragmatic pressure was measured throughout exercise. Accessory respiratory muscle oxygenation was assessed using near-infrared spectroscopy. Peak oxygen consumption, time in inspiration, time per breath and maximal inspiratory and expiratory pressures were measured in all subjects. RESULTS: The tension time index remained markedly abnormal after heart transplantation both at rest ([mean +/- SD] normal group 0.01 +/- 0.006, heart failure group 0.026 +/- 0.018, transplant group 0.058 +/- 0.015, p < 0.004) and at peak exercise (normal group 0.03 +/- 0.02, heart failure group 0.10 +/- 0.03, transplant group 0.10 +/- 0.04, p < 0.0001). Accessory respiratory muscle deoxygenation was present only in patients with heart failure (near-infrared absorbency changes [arbitrary units]: normal group -3 +/- 6, heart failure group 28 +/- 5, transplant group -3.5 +/- 4.4, p < 0.0001). CONCLUSIONS: Although heart transplantation alleviates dyspnea in patients with heart failure, the work of breathing as assessed by the tension time index of the diaphragm is not decreased. Amelioration of exertional dyspnea is achieved by other mechanisms, such as improved respiratory muscle perfusion.

Case-Control Studies↗
PubMed1996

Creatine depletion elicits structural, biochemical, and physiological adaptations in rat costal diaphragm.

To elucidate adaptations elicited by creatine (Cr) depletion in the costal diaphragm (Dia), 16 12-wk-old male Fisher 344 rats had 2% beta-guanidinopropionic acid (beta-GPA), a competitive inhibitor of Cr transport into muscle, added to their food; a control group (Con) of 16 rats ate normal rat chow. After 18 wk, beta-GPA and Con Dia did not differ histochemically with respect to fiber-type distribution; however, the cross-sectional area of type II(b + x) fibers was 33% less in beta-GPA than Con Dia. Biochemically, the proportion of myosin heavy chain IIb in beta-GPA Dia was decreased 42% from Con Dia, whereas the proportions of myosin heavy chains I and IIa were increased. Physiologically, both peak twitch tension and tetanic tension in beta-GPA Dia were decreased 40% from Con. To assess fatigability, we used the protocol of Kelsen and Nochomovitz (J. Appl. Physiol. 53; 440-447, 1982) for 2-6 min duration; the percentage of initial force exhibited by beta-GPA Dia was approximately twice that of Con Dia. We conclude that these structural, biochemical, and physiological adaptations elicited by Cr depletion can all be explained by selective atrophy of IIb muscle fibers in the Dia.

Acclimatization↗
PubMed1995

Benefit of selective respiratory muscle training on exercise capacity in patients with chronic congestive heart failure.

BACKGROUND: Diminished respiratory muscle strength and endurance have been demonstrated in patients with heart failure. This may contribute to exertional dyspnea and reduced exercise capacity in these patients. The purpose of this study was to investigate whether selective respiratory muscle training could alleviate dyspnea and improve exercise performance in patients with chronic congestive heart failure. METHODS AND RESULTS: Fourteen patients with chronic heart failure (left ventricular ejection fraction, 22 +/- 9%) were enrolled in a supervised respiratory muscle training program. This consisted of three weekly sessions of isocapnic hyperpnea at maximal sustainable ventilatory capacity, resistive breathing, and strength training. Maximum sustainable ventilatory capacity, maximum voluntary ventilation, maximal inspiratory and expiratory pressures, peak VO2, and the 6-minute walk test were measured before (pre) and after (post) 3 months of training. Eight patients completed the training program. Respiratory muscle endurance was improved with training, as evidenced by increases in maximal sustainable ventilatory capacity (pre, 48.6 +/- 10.7 versus post, 76.9 +/- 14.5 L/min; P < .05) and in maximal voluntary ventilation (pre, 100 +/- 36 versus post, 115 +/- 39 L/min; P < .05). Respiratory muscle strength was also increased with training as maximal inspiratory (pre, 64 +/- 31 versus post, 78 +/- 33 cm, H2O; P < .01) and expiratory (pre, 94 +/- 30 versus post, 133 +/- 53 cm H2O; P < .001) pressures rose. Submaximal and maximal exercise capacity were significantly improved with selective respiratory muscle training as the 6-minute walk (pre, 1101 +/- 351 versus post, 1421 +/- 328 ft; P < .001) and peak exercise VO2 (pre, 11.4 +/- 3.3 versus post, 13.3 +/- 2.7 mL.kg-1.min-1; P < .05) both significantly increased. Dyspnea during activities of daily living was subjectively improved in the majority of trained patients. Dyspnea quantified by the Borg scale was significantly reduced during progressive isocapnic hypernea but not during bicycle exercise. No statistically significant improvement in maximal sustainable ventilatory capacity, maximum voluntary ventilation, maximal inspiratory or expiratory mouth pressures, 6-minute walk, or peak VO2 was observed in the 6 patients who did not complete the training program. CONCLUSIONS: Selective respiratory muscle training improves respiratory muscle endurance and strength, with an enhancement of submaximal and maximal exercise capacity in patients with heart failure. Dyspnea during activities of daily living was subjectively improved in the majority of trained patients.

Adult↗
PubMed1994

Evidence of reduced respiratory muscle endurance in patients with heart failure.

OBJECTIVES: We sought to investigate whether reduced respiratory muscle endurance contributes to increased dyspnea and decreased exercise capacity in patients with chronic heart failure. BACKGROUND: In patients with heart failure, the sensation of dyspnea may be related to abnormalities of respiratory muscle function, such as diminished strength or endurance, or both. METHODS: Respiratory muscle endurance was assessed by measuring maximal sustainable ventilatory capacity in 15 patients with congestive heart failure and 8 normal subjects using progressive isocapnic hyperpnea. Near-infrared spectroscopy of an accessory respiratory muscle, Borg scale recordings of perceived dyspnea, time in inspiration, time per breath and minute ventilation were measured. Exercise testing with measurement of oxygen consumption was also performed. RESULTS: Maximal voluntary ventilation (normal subjects 167 +/- 40, heart failure group 89 +/- 31 liters/min) and maximal sustainable ventilatory capacity (normal subjects 90 +/- 23, heart failure group 53 +/- 22 liters/min) were significantly reduced in patients with heart failure (both p < 0.05). No significant accessory respiratory muscle deoxygenation was observed in either group. Borg scale recordings at maximal sustainable ventilatory capacity were comparable in both groups. At rest, the inspiratory duty cycle (i.e., time in inspiration divided by the time per breath) was comparable in the two groups (normal subjects 0.34 +/- 0.09, heart failure group 0.37 +/- 0.12, p = NS). However at maximal sustainable ventilatory capacity, only normal subjects had a significant increase in the inspiratory duty cycle (normal subjects 0.49 +/- 0.04, heart failure group 0.36 +/- 0.10, p < 0.05). This finding suggests obstruction to airflow in patients with congestive heart failure. Values for peak exercise minute ventilation did not differ significantly from values in maximal sustainable ventilatory capacity in either group and were significantly correlated (r = 0.84, p < 0.0001). CONCLUSION: Respiratory muscle endurance as assessed by maximal sustainable ventilatory capacity is reduced in patients with heart failure.

Adult↗
PubMed1992

Respiratory muscle function and dyspnea in patients with chronic congestive heart failure.

BACKGROUND: Patients with heart failure (HF) frequently experience exertional dyspnea. Using near-infrared spectroscopy, we have previously demonstrated accessory respiratory muscle deoxygenation during exercise in these patients by monitoring changes in light absorption at 760-800 nm. METHODS AND RESULTS: To investigate whether low-frequency respiratory muscle fatigue occurs, we performed supramaximal bilateral transcutaneous phrenic nerve stimulation before and after maximal bicycle exercise in 10 patients with HF (age, 62 +/- 10 years; ejection fraction, 18 +/- 7%) and six normal subjects (age, 50 +/- 8 years). Maximal rates of contraction and relaxation, peak twitch tension, and maximal transdiaphragmatic pressure (Pdi) were derived before and after exercise from analysis of six to 12 twitches obtained at functional residual capacity. Pdi, time in inspiration (Ti), time per breath (TTOT), respiratory gases, ratings of perceived dyspnea and fatigue, and 760-800 nm near-infrared spectroscopy absorbency changes of the serratus anterior muscle were measured throughout exercise. The tension time index (TTdi) of the diaphragm was derived. In both normal and HF subjects, all parameters of diaphragmatic function (i.e., maximal rates of contraction and relaxation, peak twitch tension, and maximal Pdi) were unchanged before and after exercise. Mean Pdi was comparable at rest (normal, 3.7 +/- 1; HF, 5.8 +/- 2.9 cm H2O; p = NS) but significantly greater in patients with HF at peak exercise (normal, 12.1 +/- 3; HF, 18.3 +/- 6.6 cm H2O; p less than 0.05). Ti/TTOT of both groups was similar at rest and throughout exercise. TTdi was significantly greater at rest (normal, 0.01 +/- 0.01; HF, 0.03 +/- 0.02; p less than 0.05) and at peak exercise (normal, 0.03 +/- 0.02; HF, 0.10 +/- 0.03; p less than 0.04) in patients with HF. Significant accessory respiration muscle deoxygenation was noted only in patients with HF (peak exercise; normal, -1 +/- 13; HF, 28 +/- 15 arbitrary units; p less than 0.01). Linear correlation analysis was performed between ratings of perceived dyspnea and parameters of pulmonary and diaphragmatic function. Significant correlations were observed between ratings of perceived dyspnea and maximal inspiratory and expiratory pressure, the TTdi of the diaphragm, near-infrared absorption changes, and forced expiratory volume in 1 second (FEV1) (all r greater than 0.5; p less than 0.05). Thus, respiratory muscle strength, work, and oxygenation were significantly correlated with the degree of dyspnea. CONCLUSIONS: We conclude that low-frequency diaphragmatic muscle fatigue does not occur despite accessory respiratory muscle deoxygenation during exercise in patients with HF. However, diaphragmatic work as assessed by the TTdi is dramatically increased in patients with HF and approaches levels previously shown to generate fatigue. The sensation of dyspnea appears closely related to respiratory muscle function.

Aged↗
PubMed1991

Use of a triaxial magnetometer for respiratory measurements.

We describe a triaxial magnetometer (Tri-mag) system, which consists of a transmitter, four sensors, a processing unit, and a personal computer (PC). The Tri-mag processing unit outputs the position of each sensor relative to the transmitter in three orthogonal coordinates, and this information is communicated to the PC. First, we demonstrated that within a defined octant of a sphere in which the center is the transmitter, we can measure radial distances with an accuracy of +/- 1 mm over a range extending from 10 to 70 cm from the transmitter. Second, we recorded the three-dimensional movement of sensors on the anterior and posterior surfaces of the chest wall during maximum voluntary ventilation in four normal men; all sensors were placed in the midsagittal plane of the body. Anterior sensors were located on the sternum at the level of the third intercostal space and at 2 cm above the umbilicus, whereas posterior sensors were located on the posterior spine at the same vertical levels as the anterior sensors. In all subjects the following was found. 1) Both anterior sensors moved anterior and cephalad during inspiration. The anterior thoracic sensor showed greater vertical than anteroposterior (A-P) movement, whereas the anterior abdominal sensor showed greater A-P than vertical movement. 2) Inspiration was associated with spinal extension, whereas expiration was associated with spinal flexion. Third, we used Tri-mag information to 1) measure tidal volume (VT) over a range extending from 500 ml to inspiratory capacity and 2) measure the change in end-expiratory lung volume (EELV) over a range extending from FRC to FRC plus a minimum of 1.5 liters. Our results indicate that greater than 96% of the changes in VT and greater than 82% of the changes in EELV can be accounted for by changes in A-P, vertical, and lateral dimensions of the chest wall.

Adult↗
PubMed1990

Negative-pressure ventilation.

In this review, we make the following major points: (1) Canine experiments indicate that in an experimental model of ARDS, cyclic NPV plus NEEP is as effective as cyclic PPV plus PEEP in treating arterial hypoxemia. Because cyclic NPV plus NEEP does not depress cardiac output as much as cyclic PPV plus PEEP, further study of this potential therapy is warranted. (2) At the present time, NPV has little use in neonatal medicine. (3) However, in adult medicine, NPV is efficacious for providing chronic ventilatory support in patients with neuromuscular and chest wall diseases. Additionally, the role of NPV in postoperative weaning warrants further study. (4) Some data in the literature suggest that some subsets of patients with CAL may benefit from chronic intermittent NPV therapy. However, criteria for identifying these patients have not been established. (5) Some investigators have recently demonstrated that PPV delivered via the nares can elicit VMR. Because this technique provides us with the opportunity to elicit VMR by a method other than NPV, nasal PPV provides us with a method to directly validate our presumption that improvements in COPD patients are related to VMR per se.

Adult↗
PubMed1988

Low-frequency diaphragmatic fatigue in spontaneously breathing humans.

We used transdiaphragmatic peak twitch tension (PTT) elicited by bilateral phrenic nerve stimulation to ascertain whether low-frequency (LF) diaphragmatic fatigue (DF) can be induced in spontaneously breathing humans by a combination of an inspiratory resistive load (IRL) and graded treadmill exercise (GXT). Our subjects were 10 young males with normal cardiopulmonary function. Before exercise we measured PTT in each subject by administering supramaximal electrical pulses of 100-microseconds duration at a frequency of 1 Hz to each phrenic nerve with the subjects breath holding at functional residual capacity at a given thoracoabdominal configuration. A minimum of six satisfactory PTT measurements were made in each subject, and we computed the 95% confidence limits (CL) for each subject. The subjects then inspired through a resistive load of 38 cmH2O.1(-1).s-1 while carrying out the GXT until exhaustion. After the GXT, PTT was remeasured in all subjects. In five of the subjects, the post-GXT mean PTT fell below the 95% CL of the pre-GXT mean PTT. However, post-GXT PTT means for the other five subjects were within the 95% CL of the pre-GXT means. In conclusion, using PTT as a measure of LFDF, these results demonstrate that LFDF can be produced in 50% of spontaneously breathing young normal males.

Adult↗
PubMed1988

Inspiratory pressure generation: comparison of subjects with COPD and age-matched normals.

We continuously monitored esophageal (Pes) and gastric (Pga) pressures and used these measurements in a three-component model to estimate instantaneous diaphragmatic (DIA), inspiratory accessory muscle (IAM), and postexpiratory recoil (PER) pressures at various times during inspiration. We validated our model both by volume-pressure relationships of the respiratory system (Vrc-Pga and Vab-Pga, where Vrc and Vab are the rib cage and abdominal volumes, respectively) as well as electromyography of the respiratory muscles. Measurements were carried out at rest and during graded treadmill exercise in 11 subjects with chronic obstructive pulmonary disease (COPDs) and 8 age-matched normal subjects (AMNs). AMNs were 59 +/- 2 (SE) yr and had a forced expiratory volume at 1 s (FEV1.0) of 3.6 +/- 0.2 liters; COPDs were 66 +/- 2 yr and had a FEV1.0 of 1.0 +/- 0.1 liters. We noted the following. At rest, both AMNs and COPDs exhibited an increasing DIA pressure (PDIA) across inspiratory time (TI) at rest. As expired minute ventilation increased with exercise intensity, AMNs continued to maintain this PDIA ramp across inspiration; in contrast, COPDs exhibited higher values of PDIA during the first half of TI than during the second half. At all intensities of exercise, COPDs exhibited higher IAM and PER pressures than the AMNs.

Age Factors↗
PubMed1988

Respiratory muscle rest therapy.

This article discusses the role of respiratory muscle rest therapy in hypercapnic ventilatory failure and/or inspiratory muscle fatigue associated with primary lung disease, diseases of the chest wall, and neuromuscular diseases. Some animal data on the role of ventilatory muscle rest therapy in states characterized by a low cardiac output and arterial hypotension are also reviewed. Additionally, a method for quantitating the degree of respiratory muscle rest elicited by negative pressure ventilation devices is presented.

Cardiac Output, Low↗
PubMed1987

Selection factors in clinical trials: results from the Community Clinical Oncology Program Physician's Patient Log.

Between August 1984 and November 1985, data concerning 44,156 newly diagnosed cancer patients were entered in the Community Clinical Oncology Program Physician's Patient Log. Forty percent (17,773 patients) had a National Cancer Institute-approved protocol available for site and stage of disease. Fifty-six percent of patients with a protocol available were clinically eligible and 19% were entered on protocol. Thus, one-third of clinically eligible patients were entered in the study. Age was a major factor influencing eligibility and entry on study. Eighty percent of patients less than 25 years of age with a protocol available were clinically eligible for clinical trials participation, and 58% were placed on protocol. Patients greater than or equal to 65 years of age with a protocol available were less likely to be clinically eligible (48%) or placed on study (14%). A physician's preference for an alternate treatment and patient refusal for protocol treatment were also important reasons that clinically eligible patients were not registered on protocol. Selection for clinical trials participation affects the characteristics of patients under study and may have an impact on the ability to generalize the results of clinical trials.

Adult↗
PubMed1986

Importance of visual field score and asymmetry in the detection of glaucoma.

The visual fields and intraocular pressures (IOP's) of 115 normal volunteers and 107 suspect/diagnosed early glaucoma subjects were recorded by Friedmann static perimetry and noncontact tonometry or applanation tonometry. The visual field data were analyzed statistically and quantified numerically by a microcomputer. The readings obtained from the suspect/diagnosed early glaucoma subjects were compared to those from an age-matched control group according to four criteria: highest field score; field score asymmetry; highest IOP; and IOP asymmetry. A combined field score and asymmetry analysis was found to be more sensitive, 86%, than a combined IOP and IOP asymmetry analysis, 56%. The combined field score and field score asymmetry analysis also gave a clear bimodal separation of subjects with early visual field defects from those with normal visual function.

Adult↗
PubMed1980

Micropachometry: a technique for measuring the thickness of the corneal epithelium.

A micropachometer was developed for the measurement of epithelial thickness in the living human cornea. The technique requires no contact with the eye and will be of value in studies of the anterior cornea and the physiological effects of contact lenses. The design is described, and results are presented from measurements of epithelial thickness.

Biometry↗
PubMed1979

A study of lobular carcinoma of the breast based on the Third National Cancer Survey in The United States of America.

Cases in in situ and infiltrating lobular carcinoma of the breast reported in the Third National Cancer Survey were reviewed according to age, sex, race, and geographic distribution. The age-specific incidence rates indicate that there are two peak age periods of risk for invasive lobular carcinoma, the first occurring in ages 40-50 years and the second after age 65. The incidence rates for lobular carcinoma were compared to the incidence rates for intraductal and infiltrating ductal carcinoma reported from the Third National Cancer Survey and for total breast cancer from the Miyagi prefecture in Japan. These comparisons indicate that factors which influence the geographic variation in breast cancer play important roles in the etiology of infiltrating ductal carcinoma, but may have little effect upon the incidence of lobular carcinoma and intraductal carcinoma. The limitations of large histological epidemiological surveys are discussed.

Adult↗
PubMed1979

Color as a variable in making an erotic film more arousing.

Eight adult male subjects participated in a counterbalanced, repeated-measures design to determine the relative efficacy of color and black-and-white visual sexual stimuli in eliciting sexual arousing, as objectively measured by a mercury-in-rubber strain gauge transducer. There were no consistent or significant differences in either the intensity of the pattern of penile responding during color and black-and-white presentations of the same film.

Adult↗