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Biomedical subjects

D Henson

Publications and source records attributed to D Henson.

At least 19 recordsLinked to original sources
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↗
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↗
PubMed1977

An epidemiologic study of cancer of the cervix, vagina, and vulva based on the Third National Cancer Survey in the United States.

Cases of invasive and in situ carcinoma of the lower female genital tract as reported in the Third National Cancer Survey in the United States were analyzed according to age, race, and geographic distribution. Results indicate that the incidence rates of in situ and invasive carcinoma of the cervix were greater in black than in white women, with a relative risk rate for black women of approximately two for both types of cervical carcinoma. For white women, the age-specific rates for invasive carcinoma of the cervix remained relatively constant after age 45, while for black women the age-specific rates for invasive carcinoma continued to increase after age 45. For both races, the patterns of age-specific incidence rates for in situ and invasive carcinoma of the cervix were not similar to those for carcinoma of the vagina or vulva. The pattern of age-specific incidence rates of adenocarcinoma of the cervix did not resemble those for in situ or invasive squamous cell carcinoma of the cervix. The rates for adenocarcinoma of the cervix demonstrated patterns similar to those for intraductal carcinoma of the breast. Results of the study are discussed in relationship to the field theory of carcinogenesis as developed for the lower female genital tract.

Adenocarcinoma↗
PubMed1972

Chronic infection of the rabbit central nervous system by a slowly growing equine herpesvirus.

The spinal cords of rabbits were chronically infected by a slowly growing horse herpesvirus (a "cytomegalovirus") inoculated directly therein. Virus was recovered from the central nervous systems of some of such animals after more than 1 year. The virus could be reisolated from all the animals killed during the first few weeks after its injection; acute focal meningomyelitis was present with involvement of gray and white matter of the cervical, thoracic, and lumbar levels of the spinal cords of these rabbits, though the nerve cells themselves remained undamaged. Thereafter, reisolation of the virus became sporadic, and no damage to the spinal cord could be histologically discerned even in animals from which the virus was recovered. No paralytic or other clinical effects could be attributed to the infection.

Animals↗