Microgravity decreases heart rate and arterial pressure in humans

Spaceflight causes adaptive changes in cardiovascular physiology, such as postflight orthostatic intolerance, that can have deleterious effects on astronauts. In-flight cardiovascular data are difficult to obtain, and results have been inconsistent. To determine normative in-flight changes in Shuttle astronauts, we measured heart rate, arterial pressure, and cardiac rhythm disturbances for 24-h periods before, during, and after spaceflight on Shuttle astronauts performing their normal routines. We found that heart rate, diastolic pressure, variability of heart rate and diastolic pressure, and premature ventricular contractions all were significantly reduced in flight. Systolic pressure and premature atrial contractions also tended to be reduced in flight. These data constitute the first systematic evaluation of in-flight changes in basic cardiovascular variables in Shuttle astronauts and suggest that a microgravity environment itself does not present a chronic stress to the cardiovascular system.

Phase-encode reordering to minimize errors caused by motion

A new method for suppressing the effects of motion in MR images by reordering the acquisition of k space has been developed. Existing reordering methods suffer from image blurring. The method presented here applies specifically to translation along the phase-encoding direction, in which case it reduces both ghosting and blurring. The method is conceptually similar to a linear phase shift of k space, except that it has the advantage of not corrupting stationary structures inadvertently. The method is intended for anatomic sites in which substantial translational motion occurs along the phase-encoding direction, such as the cranial-caudal motion of the liver and kidneys. The reordering method is motivated from an analysis of factors affecting the severity of motion artifacts. The theory behind the reordering method is described and validated experimentally by imaging a moving phantom.

Willingness to follow breast cancer. Survey of family physicians

OBJECTIVE

To identify the experience and willingness of family physicians to accept follow-up care of patients treated for stage I breast cancer.

DESIGN

Mailed questionnaire.

PARTICIPANTS

One hundred eighty-nine family physicians in southwestern Ontario with oversampling of female physicians and physicians practising more than 20 km from a cancer clinic.

MAIN OUTCOME MEASURE

Willingness to follow breast cancer patients and time after treatment family physicians would be willing to begin follow-up care.

RESULTS

We had an 81.5% response rate. Of the 154 respondents, 53% had been involved previously in the 5-year, follow-up care of a patient with breast cancer and 77.1% believed it appropriate for family physicians to assume responsibility for follow-up care in all or most cases. If asked by a patient, the family, or an oncologist to provide follow-up care, 90.1% of family physicians reported they would accept this responsibility. Willingness to follow breast cancer patients was not associated with sex, years in practice, proximity to a cancer clinic, or certification status but was associated with having previously provided such care (P = .043). Of those willing to care for these patients, almost 90% would prefer to start within 1 year of treatment.

CONCLUSION

Although only half the respondents had experience in providing follow-up care to breast cancer patients, most were willing to take on this role, especially if asked.

fMRI of human somatosensory and cingulate cortex during painful electrical nerve stimulation

Functional MRI (fMRI) can detect changes from resting levels of blood flow and oxygenation during task performance (i.e. activation). We used a simple electrical nerve stimulation technique together with fMRI to study pain process in the human cortex. Images of the primary somatosensory (SI) and cingulate cortex (Cg) were obtained from subjects during stimulation at painful and non-painful intensities. Stimuli that evoked non-painful tingling sensations activated the contralateral SI but not Cg. Stimuli that evoked painful sensations activated both the contralateral SI and Cg. These data indicate that fMRI can detect pain-related changes in SI and Cg evoked by electrical stimulation of peripheral nerves. These findings add to the evidence for a role of SI and Cg in human pain processes and provide a simple method of stimulus delivery for its study.

Induction of tolerance to skin allografts by intrathymic injection of donor splenocytes. Effect of donor-recipient strain combination and supplemental rapamycin

The effect of donor-recipient strain combination and supplemental rapamycin (Rapa) on tolerance induction by intrathymic (IT) injection of donor splenocytes was examined in a mouse skin allograft model. In an MHC class I-mismatched C3H/He skin to (C57BL/6 x A)F1 (B6AF1) mouse combination, IT injection of 50 x 10(6) donor splenocytes with transient immunosuppression by rabbit anti-mouse lymphocyte serum (ALS) induced significant prolongation of skin allograft survival with a median survival time (MST) of 115 days versus an MST of 24.5 days in controls given ALS alone. With an additional short course of supplemental Rapa treatment at a dose of 1.5 mg/kg i.p. every other day from day 0 to 12, all C3H/He skin allografts survived indefinitely (> 350 days) in ALS-treated, donor splenocyte intrathymically injected B6AF1 recipient mice. Tolerance was antigen-specific, since the second donor-type skin allografts were accepted while third-party skin allografts were acutely rejected in these mice bearing long-term C3H/He skin allografts. In MHC class I- and II-disparate (DBA/2 to B6AF1) and fully MHC-incompatible (AKR to B6) strain combinations, IT injection of donor splenocytes and ALS treatment failed to prolong skin allograft survival over ALS controls. When supplemental Rapa was used, long-term skin allograft acceptance was observed with an MST of 127 days for the DBA/2 to B6AF1 combination and 70 days for the AKR to B6 combination. In contrast, supplemental treatment with cyclosporine was not effective in these combinations, which suggests that supplemental Rapa may have a unique effect in augmenting IT tolerance induction. Thymectomy within 7 days after IT injection significantly shortened the allograft survival, which suggests that interaction of the host thymus and the injected donor splenocytes, which takes place early after IT injection, plays an important role in the induction of allograft tolerance in this model.

Who provides follow-up care for patients with early breast cancer?

OBJECTIVE

To assess how often family physicians are involved in posttreatment care of their stage I breast cancer patients and to identify factors associated with family physicians providing follow-up care.

DESIGN

A retrospective cohort study with a 5-year follow up by chart review.

PARTICIPANTS

All cases of breast cancer seen at the London Regional Cancer Centre between 1982 and 1987 were reviewed to identify 183 stage I cancer patients alive at 5 years.

MAIN OUTCOME MEASURES

Whether a physician (other than an oncologist) was involved in the follow-up care of patients, and whether the physician was a family physician or a surgeon.

RESULTS

Follow-up care during the 5-year postoperative period was provided in most cases by oncologists alone (66.7%); family physicians and surgeons were involved in 17.5% and 15.8% of cases, respectively. Surgeons became involved in follow-up care much earlier (12 months) than family physicians did (23 months) (P = 0.01) and were more likely to provide care for patients who received radiation treatment (P = 0.04) and for patients who lived in London (P = 0.004). Most malignant breast lesions (77.5%) were discovered by patients themselves (P = 0.0001).

CONCLUSIONS

Currently, family physicians are infrequently involved in follow-up care of their patients with early breast cancer.

Marked prolongation of rat skin xenografts induced by intrathymic injection of xenogeneic splenocytes and a short course of rapamycin in antilymphocyte serum-treated mice

The effect of intrathymic (IT) injection of donor splenocytes and a short course of rapamycin (Rapa) treatment on rat to mouse skin xenograft survival was investigated. ACI rat skin xenografts were transplanted to (C57BL/6 x A)F1 mice treated with rabbit anti-mouse lymphocyte serum (ALS) on days -1, +2, and +4 relative to skin grafting on day 0. Fifty million donor-type splenocytes were injected intrathymically on day 7 after transplantation. Rapa was given intraperitoneally every other day from day 0 to day 12 at a dose of 3.0 mg/kg. Prolonged skin xenograft survival was observed in ALS- and Rapa-treated recipients (no IT injection) with a median survival time of 47 days. However, skin graft survival was markedly more prolonged in the group treated with ALS, Rapa, and IT injection of donor splenocytes did not have a beneficial effect on skin xenograft survival in ALS-treated recipients. An increased presence of donor-type cells was observed in the thymus of the ALS- and Rapa-treated recipients for 7 days after IT injection of donor splenocytes. In conclusion, a short course of Rapa markedly augments rat skin xenograft survival in ALS-treated mice injected intrathymically with donor-type splenocytes.

Analysis of donor reactive cells in ALS-treated mice bearing skin allografts after the intrathymic injection of donor specific spleen cells

The intrathymic injection of donor spleen cells into antilymphocyte serum (ALS)-treated mice induces significant prolongation of donor skin grafts. The intrathymic route of antigen presentation in this model is superior to the intravenous route in achieving unresponsiveness. To elucidate possible mechanisms involved in the induction of unresponsiveness in ALS-treated mice after intrathymic injection of donor spleen cells, we have analysed the reactivity of lymphoid cells from unresponsive mice in various ways. Deletion of donor reactive cells has been studied using the Mls antigen system. Functional inactivation was analysed by a sequential study of the frequency of donor reactive cells. Suppressor cell activity was studied using an adoptive transfer assay. Deletion of donor reactive cells was partial and occurred largely in the spleen in both early and late stages of unresponsiveness. The frequency of donor reactive cytotoxic cells was suppressed in both spleen and lymph nodes from day +/- 13 until grafts were rejected, with the exception of a rebound period at day +/- 22. In contrast, donor reactive cells were not deleted or inactivated in the thymus. Suppressor cell activity could only be detected in mice bearing long-term grafts. These results suggest that donor reactive cytotoxic cells are functionally inactivated in the spleen and nodes in the early and late stages of unresponsiveness after intrathymic injection of antigen. In contrast, donor reactive cells in the thymus do not appear to be affected.

Planar-motion correction with use of K-space data acquired in Fourier MR imaging

The authors have developed a method for reducing magnetic resonance (MR) image artifacts caused by planar motion. Segments of k-space acquired with the subject stationary are detected automatically. Each k-space segment is Fourier transformed into an image in which rotational and translational displacements are measured manually. Before correction, k-space is made as Hermitian as allowed by the largest symmetric range of low spatial frequencies acquired with the subject stationary. Segments of k-space acquired with the subject in different positions are corrected separately. Although translation corrections can be applied effectively to both k-space and the spatial domain, rotation corrections are applied in the spatial domain to avoid image artifacts. To complement the correction, data corrupted by rotation are replaced by the complex conjugate of data of the opposite kappa x and kappa y, provided that these data have not been corrupted by rotation. The method reduced ghosts and blurring substantially on sagittal head images acquired with a standard spin-echo pulse sequence while a volunteer subject nodded his head.

Effects of head-down bed rest on complex heart rate variability: response to LBNP testing

Head-down bed rest is used to model physiological changes during spaceflight. We postulated that bed rest would decrease the degree of complex physiological heart rate variability. We analyzed continuous heart rate data from digitized Holter recordings in eight healthy female volunteers (age 28-34 yr) who underwent a 13-day 6 degree head-down bed rest study with serial lower body negative pressure (LBNP) trials. Heart rate variability was measured on 4-min data sets using conventional time and frequency domain measures as well as with a new measure of signal "complexity" (approximate entropy). Data were obtained pre-bed rest (control), during bed rest (day 4 and day 9 or 11), and 2 days post-bed rest (recovery). Tolerance to LBNP was significantly (P < 0.02) reduced on both bed rest days vs. pre-bed rest. Heart rate variability was assessed at peak LBNP. Heart rate approximate entropy was significantly (P < 0.05) decreased at day 4 and day 9 or 11, returning toward normal during recovery. Heart rate standard deviation and the ratio of high- to low-power frequency did not change significantly. We conclude that short-term bed rest is associated with a decrease in the complex variability of heart rate during LBNP testing in healthy young adult women. Measurement of heart rate complexity, using a method derived from nonlinear dynamics ("chaos theory"), may provide a sensitive marker of this loss of physiological variability, complementing conventional time and frequency domain statistical measures.

Oscillatory motion of the normal cervical spinal cord

PURPOSE

To determine the normal pattern of cervical spinal cord motion with measurement of cervical spinal cord velocity by means of phase-contrast magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Spinal cord velocity was measured in 11 healthy subjects with a modified gradient-echo pulse sequence on a conventional 1.5-T MR imaging system that generated phase images sensitive to slow motion. Prospective electrocardiogram gating was used to assess velocity as a function of the cardiac cycle. The accuracy of velocity measurements was estimated with images of a phantom moving at constant velocity.

RESULTS

The cervical spinal cord moves with an oscillatory pattern in the craniocaudal direction. The maximum velocity (7.0 mm/sec +/- 1.4 [standard deviation]) in the caudal direction occurred approximately 109 msec +/- 20 after electrical cardiac systole. The maximum velocities in subsequent oscillations decreased toward zero before the next cardiac systole.

CONCLUSION

The cervical spinal cord oscillates in a craniocaudal direction after each cardiac systole.

The haemodynamic response to the insertion of the laryngeal mask airway: a comparison with laryngoscopy and tracheal intubation

The haemodynamic response to the insertion of the laryngeal mask airway (LMA) was assessed and compared to that of laryngoscopy and tracheal intubation in a study of forty patients (ASA 1) randomly allocated into two groups and anaesthetised using a standard balanced anaesthetic technique. The results show that the changes in all cardiovascular parameters measured following LMA insertion were significantly less (P < 0.05) when compared with those following laryngoscopy and tracheal intubation. We conclude that airway management with the LMA may be used to avoid the haemodynamic response to tracheal intubation where such a response is undesirable.

A survey of nasotracheal intubating skills among Advanced Trauma Life Support course graduates

The American College of Surgeons' Advanced Trauma Life Support procedure teaches that blind nasotracheal intubation should be performed in the presence of a suspected or proven cervical spine injury in an unconscious but breathing patient who requires an artificial airway. We studied a group of non-anaesthetically trained graduates of the Advanced Trauma Life Support course and examined their skill in performing blind nasal intubations. Only six in 90 attempts were successful. We conclude that, in British hospitals, blind nasotracheal intubation should not be recommended as the first line management in securing the airway of patients with suspected or proven cervical spine injury. Alternative techniques such as bag-and-mask ventilation with cricoid pressure or a laryngeal mask airway with cricoid pressure should be adopted until oral intubation with in-line traction is performed.

Mutagenic and genotoxic effects of three vinyl chloride-induced DNA lesions: 1,N6-ethenoadenine, 3,N4-ethenocytosine, and 4-amino-5-(imidazol-2-yl)imidazole

The mutagenic and genotoxic properties of 1,N6-ethenoadenine (epsilon Ade), 3,N4-ethenocytosine (epsilon Cyt), and 4-amino-5-(imidazol-2-yl)imidazole (beta) were investigated in vivo. The former two modified bases are known DNA adducts formed by the human carcinogen vinyl chloride; beta is formed by pyrimidine ring-opening of epsilon Ade. Chemically synthesized deoxyhexanucleotides containing epsilon Ade and beta, d[GCT-(epsilon A)GC], and d[GCT(beta)GC], respectively, were described previously [Biochemistry (1987) 26, 5626-5635]. epsilon Cyt was inserted into an oligonucleotide, d[GCTAG(epsilon C)], by a mild enzymatic synthetic procedure, which avoided exposure of the base to alkaline conditions. 3,N4-Etheno-2'-deoxycytidine 3',5'-bisphosphate coupled with reasonable efficiency (30-40%) to the 3'-nucleoside of an acceptor pentamer, d(GCTAG), in a reaction catalyzed by T4 RNA ligase in the presence of ATP. Each of the three modified hexanucleotides and an unmodified control were inserted into a six-base gap positioned at a known site in the genome of bacteriophage M13-NheI. A nick was placed in the DNA strand opposite that containing the single DNA lesions, enabling the formation of singly adducted single-stranded genomes by denaturation. After transfection of the adducted phage DNAs into Escherichia coli, each of the adducts was found to be genotoxic. The most toxic lesion was beta, which reduced survival of the genome by 97%. epsilon Cyt and epsilon Ade reduced survival by 90% and 65%, respectively. An examination of the surviving phage populations revealed that each of the three adducts was mutagenic. The least mutagenic lesion was epsilon Ade (0.1% of the survivors were mutant), which showed primarily A-->G transitions.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between the chemical structures and mutagenic specificities of the DNA lesions formed by chemical and physical mutagens

The mutagenic activities of radiation, alkylating agents, and aromatic amines and amides are examined from the perspective of relating the observed patterns of mutagenesis with the structures of the premutagenic DNA lesions. The general approach taken to establish such relationships has involved the construction of viral or plasmid genomes containing specific DNA adducts. The in vivo replication of such site-specifically modified genomes results in the induction of mutations, which are characterized by DNA sequencing. It is found that the mutation types that arise in these simple systems often match those occurring in tumors produced in mammals exposed intentionally or unintentionally to carcinogenic agents.

Proton relaxation enhancement

Paramagnetic and superparamagnetic substances are used as contrast agents to enhance proton relaxation in magnetic resonance imaging. This review summarizes the physics of contrast agents, specifically the mechanisms by which contrast agents enhance T1 and T2 relaxation. The purpose is to provide a background for understanding the behavior of existing contrast agents in basic experimental and clinical studies. Terms such as magnetic dipole, dipole moment, magnetic susceptibility, diamagnetism, paramagnetism, superparamagnetism, and ferromagnetism are introduced. Two important interactions between the magnetic dipole moments of paramagnetic substances and the dipole moments associated with protons are described. The Solomon-Bloembergen-Morgan equations and other basic relaxation theory that has been confirmed experimentally are introduced to account for the dependence of relaxation on such parameters as the Larmor frequency, magnetic moment, accessibility of water molecules to the core of a contrast agent, and frequency of molecular motions.

Communication between cancer specialists and family doctors

In a qualitative study using focus group interviews, family physicians in London, Ont, were asked to describe how they perceived their role in follow-up cancer patient care. Barriers to fulfilling this role existed both in the tertiary cancer care setting and among the family physicians themselves. Suggestions for overcoming these barriers were generated.

Focus Group Interview in Family Practice Research: Implementing a qualitative research method

Focus group interviews, described as a qualitative research method with good potential in family medicine, are traced from their origins in market research to their growing role in sociology and medicine. Features of this method are described, including design, conduct, and analysis. Both proven and potential areas for primary care research using focus groups are outlined.

Genetic effects of oxidative DNA damage: comparative mutagenesis of 7,8-dihydro-8-oxoguanine and 7,8-dihydro-8-oxoadenine in Escherichia coli

A single 7,8-dihydro-8-oxoguanine (G8-OXO; 8-hydroxyguanine) adduct in the lacZ alpha gene of bacteriophage M13 DNA induces a targeted G-->T transversion after replication in Escherichia coli (Biochemistry, 29, 7024-7031 (1990)). This mutation is thought to be due to the facile formation during DNA synthesis of a G8-OXO.base pair, where G8-OXO is in the syn conformation about the deoxyglycosyl bond. A related modified purine, 7,8-dihydro-8-oxoadenine (A8-OXO; 8-hydroxyadenine), is an abundant product found in irradiated and oxidized DNAs. Similar to G8-OXO, as a mononucleoside A8-OXO assumes the syn conformation. This work has assessed the relative mutagenicities of A8-OXO and G8-OXO in the same experimental system. A deoxypentanucleotide containing A8-OXO [d(GCT-A8-OXOG)] was synthesized. After 5'-phosphorylation with [gamma-32P] ATP, the oligomer was ligated into a duplex M13mp19-derived genome at a unique NheI restriction site. Genomes containing either A8-OXO (at position 6275, [+] strand) or G8-OXO (position 6276) were denatured with heat and introduced into E.coli DL7 cells. Analysis of phage DNA from mutant plaques obtained by plating immediately after transformation (infective centers assay) revealed that G8-OXO induced G-->T transversions at an apparent frequency of approximately 0.3%. The frequency and spectrum of mutations observed in DNA sequences derived from 172 mutant plaques arising from the A8-OXO-modified DNA were almost indistiguishable from those generated from transfection of an adenine-containing control genome. We conclude that A8-OXO is at least an order of magnitude less mutagenic than G8-OXO in E.coli cells with normal DNA repair capabilities.

The effect of injection of donor bone marrow on the frequency of donor-reactive CTL in antilymphocyte serum-treated, grafted mice

The survival of C3H/He skin grafts can be prolonged on B6AF1 mice immunosuppressed with ALS by the injection of C3H/He marrow 1 week postgrafting. The precursor frequencies of donor-reactive CTL in the spleen and lymph nodes of ALS-treated, grafted mice given donor marrow were compared with CTL frequencies observed in ALS-treated, grafted controls. Spleens and nodes were removed from experimental and control mice on days +8, +14, +21, +58, and 1 year postgrafting, and used as effectors in the LDA. Donor-reactive CTL in the marrow-injected group remained suppressed as long as the recipients maintained their grafts. The frequency of CTL to third-party antigens was normal in mice bearing long-term C3H/He grafts. When marrow-injected mice rejected their grafts, the total donor-reactive CTL frequency returned to normal. In contrast, in ALS-treated controls that did not receive marrow, the total number of donor-reactive CTL returned to normal levels with recovery from the immunosuppressive effects of ALS. These results suggest that donor marrow suppresses the regeneration of donor-reactive CTL in the lymphoid tissues of ALS-treated mice, possibly by veto cell activity.